Context: dotnet/maui#11605
Context: dotnet/maui#11387 (comment)
Context: http://github.com/xamarin/xamarin-android/commit/8bc7a3e84f95e70fe12790ac31ecd97957771cb2

In dotnet/maui#11605, when `$(AndroidEnableMarshalMethods)`=True
(dotnet/android@8bc7a3e8), the build may fail if the `.sln`
contains more than one Android "App" project.  We tracked this down
to "undesired sharing" between project builds; the `obj` provided to
[`IBuildEngine4.RegisterTaskObject()`][0] can be visible across
project builds.  Consider [`<GeneratePackageManagerJava/>`][1]:

	var marshalMethodsState = BuildEngine4.GetRegisteredTaskObjectAssemblyLocal<MarshalMethodsState> (".:!MarshalMethods!:.", RegisteredTaskObjectLifetime.Build);

Further consider a `.sln` with two "App" projects, as the "App"
project build hits `<GeneratePackageManagerJava/>`.
The lifetime of `.Build` is *not* tied to the the `Build` target of a
given `.csproj`; rather, it's for the *build process*.  This can
result in:

 1. `dotnet build Project.sln` is run; `Project.sln` references
    `App1.csproj` and `App2.csproj`.
 2. `App1.csproj` is built.
 3. `App1.csproj` calls `<GeneratePackageManagerJava/>`.
 4. `App2.csproj` is later built as part in the process, and *also*
    calls `<GeneratePackageManagerJava/>`.

In particular note the key within `<GeneratePackageManagerJava/>`:
`".:!MarshalMethods!:."`.  This value is unchanged, and means that
that when `App2.csproj` is built, it will be using the same key as
was used with `App1.csproj`, and thus could be inadvertently using
data intended for `App1.csproj`!

This would result build errors:

	…\Xamarin.Android.Common.targets(1717,3): error XAGPM7009: System.InvalidOperationException: Unable to translate assembly name 'Xamarin.AndroidX.Activity' to its index
	…\Xamarin.Android.Common.targets(1717,3): error XAGPM7009:    at Xamarin.Android.Tasks.MarshalMethodsNativeAssemblyGenerator.WriteNativeMethods(LlvmIrGenerator generator, Dictionary`2 asmNameToIndex, LlvmIrVariableReference get_function_pointer_ref)
	…\Xamarin.Android.Common.targets(1717,3): error XAGPM7009:    at Xamarin.Android.Tasks.MarshalMethodsNativeAssemblyGenerator.Write(LlvmIrGenerator generator)
	…\Xamarin.Android.Common.targets(1717,3): error XAGPM7009:    at Xamarin.Android.Tasks.LLVMIR.LlvmIrComposer.Write(AndroidTargetArch arch, StreamWriter output, String fileName)
	…\Xamarin.Android.Common.targets(1717,3): error XAGPM7009:    at Xamarin.Android.Tasks.GeneratePackageManagerJava.AddEnvironment()
	…\Xamarin.Android.Common.targets(1717,3): error XAGPM7009:    at Xamarin.Android.Tasks.GeneratePackageManagerJava.RunTask()

The sharing of `RegisterTaskObject` data across project builds is
rarely desirable.  There are a few instances where it is safe to share
the registered objects between projects, e.g. `java` version
information (keyed on `java` path).  However, most of the time it is
specific to the project that is being built.  Historically we have
probably got away with this because "most" users only have one project.

Update the `MSBuildExtensions` extension methods to include an
additional `RegisterTaskObjectKeyFlags` parameter:

	[Flags]
	public enum RegisterTaskObjectKeyFlags {
		None = 0,
		IncludeProjectFile = 1 << 0,
	}

Allowing:

	var marshalMethodsState = BuildEngine4.GetRegisteredTaskObjectAssemblyLocal<MarshalMethodsState> (
	        ".:!MarshalMethods!:.",
	        RegisteredTaskObjectLifetime.Build,
	        RegisterTaskObjectKeyFlags.IncludeProjectFile
	);

When `RegisterTaskObjectKeyFlags.IncludeProjectFile` is specified,
then [`IBuildEngine.ProjectFileOfTaskNode`][2] is used as part of
the key with `RegisterTaskObject()`.  This helps ensure that builds
in different `.csproj` files will result in different keys.

The previous `MSBuildExtensions.GetRegisteredTaskObjectAssemblyLocal()`
and related overloads have been updated so that
`RegisterTaskObjectKeyFlags.IncludeProjectFile` is used by default.

[0]: https://learn.microsoft.com/en-us/dotnet/api/microsoft.build.framework.ibuildengine4.registertaskobject?view=msbuild-17-netcore
[1]: https://github.com/xamarin/xamarin-android/blob/c92ae5eb9fdcb3a2fd7c20f5b42dddf8b3ea781a/src/Xamarin.Android.Build.Tasks/Tasks/GeneratePackageManagerJava.cs#L407
[2]: https://learn.microsoft.com/en-us/dotnet/api/microsoft.build.framework.ibuildengine.projectfileoftasknode?view=msbuild-17-netcore

Context: 76c076f

When attempting to update xamarin/xamarin-android to use 4ea2d5ad,
lots of CS0121 errors appeared:

	…/src/Xamarin.Android.Build.Tasks/Tasks/FilterAssemblies.cs(80,18): error CS0121: The call is ambiguous between the following methods or properties: 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool)' and 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool, RegisterTaskObjectKeyFlags)'
	…/src/Xamarin.Android.Build.Tasks/Tasks/FilterAssemblies.cs(87,18): error CS0121: The call is ambiguous between the following methods or properties: 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool)' and 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool, RegisterTaskObjectKeyFlags)'
	…/src/Xamarin.Android.Build.Tasks/Tasks/FilterAssemblies.cs(94,18): error CS0121: The call is ambiguous between the following methods or properties: 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool)' and 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool, RegisterTaskObjectKeyFlags)'
	…/src/Xamarin.Android.Build.Tasks/Tasks/FilterAssemblies.cs(98,17): error CS0121: The call is ambiguous between the following methods or properties: 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool)' and 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool, RegisterTaskObjectKeyFlags)'
	…/src/Xamarin.Android.Build.Tasks/Tasks/GenerateCompressedAssembliesNativeSourceFiles.cs(72,17): error CS0121: The call is ambiguous between the following methods or properties: 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool)' and 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool, RegisterTaskObjectKeyFlags)'
	…/src/Xamarin.Android.Build.Tasks/Tasks/GenerateJniRemappingNativeCode.cs(95,17): error CS0121: The call is ambiguous between the following methods or properties: 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool)' and 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool, RegisterTaskObjectKeyFlags)'
	…/src/Xamarin.Android.Build.Tasks/Tasks/WriteLockFile.cs(35,19): error CS0121: The call is ambiguous between the following methods or properties: 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool)' and 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool, RegisterTaskObjectKeyFlags)'
	…/src/Xamarin.Android.Build.Tasks/Tasks/GenerateJavaStubs.cs(524,18): error CS0121: The call is ambiguous between the following methods or properties: 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool)' and 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool, RegisterTaskObjectKeyFlags)'
	…/src/Xamarin.Android.Build.Tasks/Tasks/GenerateJavaStubs.cs(578,17): error CS0121: The call is ambiguous between the following methods or properties: 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool)' and 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool, RegisterTaskObjectKeyFlags)'
	…/src/Xamarin.Android.Build.Tasks/Utilities/MonoAndroidHelper.cs(393,11): error CS0121: The call is ambiguous between the following methods or properties: 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool)' and 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool, RegisterTaskObjectKeyFlags)'
	…/src/Xamarin.Android.Build.Tasks/Utilities/MonoAndroidHelper.cs(440,11): error CS0121: The call is ambiguous between the following methods or properties: 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool)' and 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool, RegisterTaskObjectKeyFlags)'
	…/src/Xamarin.Android.Build.Tasks/Utilities/MonoAndroidHelper.cs(501,11): error CS0121: The call is ambiguous between the following methods or properties: 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool)' and 'MSBuildExtensions.RegisterTaskObjectAssemblyLocal(IBuildEngine4, object, object, RegisteredTaskObjectLifetime, bool, RegisterTaskObjectKeyFlags)'

This is because when given e.g.:

	partial class MSBuildExtensions {
	    public static void RegisterTaskObjectAssemblyLocal (this IBuildEngine4 engine, object key, object value, RegisteredTaskObjectLifetime lifetime, bool allowEarlyCollection = false);
	    public static void RegisterTaskObjectAssemblyLocal (this IBuildEngine4 engine, object key, object value, RegisteredTaskObjectLifetime lifetime, bool allowEarlyCollection = false, RegisterTaskObjectKeyFlags flags = RegisterTaskObjectKeyFlags.IncludeProjectFile);
	}

then this expression:

	engine.RegisterTaskObjectAssemblyLocal(key, value, lifetime);

has two possible matches, due to the default parameters.

Fix this by *removing* the default `RegisteredTaskObjectLifetime`
parameter value, and (when appropriate) adding an overload:

	partial class MSBuildExtensions {
	    public static void RegisterTaskObjectAssemblyLocal (this IBuildEngine4 engine, object key, object value, RegisteredTaskObjectLifetime lifetime, bool allowEarlyCollection = false);
	    public static void RegisterTaskObjectAssemblyLocal (this IBuildEngine4 engine, object key, object value, RegisteredTaskObjectLifetime lifetime, RegisterTaskObjectKeyFlags flagse);
	    public static void RegisterTaskObjectAssemblyLocal (this IBuildEngine4 engine, object key, object value, RegisteredTaskObjectLifetime lifetime, bool allowEarlyCollection, RegisterTaskObjectKeyFlags flags);
	}

Additionally, *remove* the `[Obsolete]` attributes.  With
`RegisterTaskObjectKeyFlags.IncludeProjectFile` part of the default
behavior, there is no need to mark the original methods `[Obsolete]`.
This allows existing code such as:

	var value = BuildEngine4.GetRegisteredTaskObjectAssemblyLocal (key, Lifetime);

to remain unchanged.

Reverts: 47f95ab
Reverts: 76c076f

Context: dotnet/android#7685 (comment)

The problem is that we misunderstood
[`IBuildEngine.ProjectFileOfTaskNode`][0]: we *thought* (hoped?) that
it would return `$(MSBuildProjectFullPath)`, the path to the
`.csproj` being built.

In actuality it returns `$(MSBuildThisFileFullPath)` for the file
containing the Task invocation.  Meaning if e.g.
`Xamarin.Android.Common.targets` contains the Task invocation, then
IBuildEngine.ProjectFileOfTaskNode` would be the path to
`Xamarin.Android.Common.targets`, *not* the path of the `.csproj`.

This in turn means it doesn't actually solve the problem we had.

We will instead need to audit all use of
`IBuildEngine4.RegisterTaskObject()` & related to ensure that the
keys provided *also* contain paths to project-specific files,
if necessary.

Revert 47f95ab and 76c076f, as the changes are not needed.

[0]: https://learn.microsoft.com/en-us/dotnet/api/microsoft.build.framework.ibuildengine.projectfileoftasknode?view=msbuild-17-netcore

…#202)

Context: dotnet/maui#11605
Context: dotnet/maui#11387 (comment)
Context: http://github.com/xamarin/xamarin-android/commit/8bc7a3e84f95e70fe12790ac31ecd97957771cb2

In dotnet/maui#11605, when `$(AndroidEnableMarshalMethods)`=True
(dotnet/android@8bc7a3e8), the build may fail if the `.sln`
contains more than one Android "App" project.  We tracked this down
to "undesired sharing" between project builds; the `obj` provided to
[`IBuildEngine4.RegisterTaskObject()`][0] can be visible across
project builds.  Consider [`<GeneratePackageManagerJava/>`][1]:

	var marshalMethodsState = BuildEngine4.GetRegisteredTaskObjectAssemblyLocal<MarshalMethodsState> (".:!MarshalMethods!:.", RegisteredTaskObjectLifetime.Build);

Further consider a `.sln` with two "App" projects, as the "App"
project build hits `<GeneratePackageManagerJava/>`.
The lifetime of `.Build` is *not* tied to the the `Build` target of a
given `.csproj`; rather, it's for the *build process*.  This can
result in:

 1. `dotnet build Project.sln` is run; `Project.sln` references
    `App1.csproj` and `App2.csproj`.
 2. `App1.csproj` is built.
 3. `App1.csproj` calls `<GeneratePackageManagerJava/>`.
 4. `App2.csproj` is later built as part of the process, and *also*
    calls `<GeneratePackageManagerJava/>`.

In particular note the key within `<GeneratePackageManagerJava/>`:
`".:!MarshalMethods!:."`.  This value is identical in all projects,
and means that that when `App2.csproj` is built, it will be using the
same key as was used with `App1.csproj`, and thus could be
inadvertently using data intended for `App1.csproj`!

This would result build errors:

	…\Xamarin.Android.Common.targets(1717,3): error XAGPM7009: System.InvalidOperationException: Unable to translate assembly name 'Xamarin.AndroidX.Activity' to its index
	…\Xamarin.Android.Common.targets(1717,3): error XAGPM7009:    at Xamarin.Android.Tasks.MarshalMethodsNativeAssemblyGenerator.WriteNativeMethods(LlvmIrGenerator generator, Dictionary`2 asmNameToIndex, LlvmIrVariableReference get_function_pointer_ref)
	…\Xamarin.Android.Common.targets(1717,3): error XAGPM7009:    at Xamarin.Android.Tasks.MarshalMethodsNativeAssemblyGenerator.Write(LlvmIrGenerator generator)
	…\Xamarin.Android.Common.targets(1717,3): error XAGPM7009:    at Xamarin.Android.Tasks.LLVMIR.LlvmIrComposer.Write(AndroidTargetArch arch, StreamWriter output, String fileName)
	…\Xamarin.Android.Common.targets(1717,3): error XAGPM7009:    at Xamarin.Android.Tasks.GeneratePackageManagerJava.AddEnvironment()
	…\Xamarin.Android.Common.targets(1717,3): error XAGPM7009:    at Xamarin.Android.Tasks.GeneratePackageManagerJava.RunTask()

The sharing of `RegisterTaskObject()` data across project builds is
rarely desirable.  There are a few instances where it is safe to share
the registered objects between projects, e.g. `java -version` version
information (keyed on `java` path).  However, most of the time it is
specific to the project that is being built.  Historically we have
probably got away with this because "most" users only have one project.

Update `AndroidTask` and `AndroidToolTask` to capture the current
directory in a `WorkingDirectory` property like [`AsyncTask`][2] does.
Introduce new `ProjectSpecificTaskObjectKey()` instance methods into
`AndroidTask`, `AndroidAsyncTask`, and `AndroidToolTask` which can be
used to generate a key which includes `WorkingDirectory`.  This allows:

	var marshalMethodsState = BuildEngine4.GetRegisteredTaskObjectAssemblyLocal<MarshalMethodsState> (
	        ProjectSpecificTaskObjectKey (".:!MarshalMethods!:."),
	        RegisteredTaskObjectLifetime.Build
	);

When `ProjectSpecificTaskObjectKey()` is used the `WorkingDirectory`
is included in the key with `RegisterTaskObject()`.  This helps ensure
that builds in different `.csproj` files will result in different keys.

[0]: https://learn.microsoft.com/en-us/dotnet/api/microsoft.build.framework.ibuildengine4.registertaskobject?view=msbuild-17-netcore
[1]: https://github.com/xamarin/xamarin-android/blob/c92ae5eb9fdcb3a2fd7c20f5b42dddf8b3ea781a/src/Xamarin.Android.Build.Tasks/Tasks/GeneratePackageManagerJava.cs#L407
[2]: https://github.com/xamarin/Xamarin.Build.AsyncTask/blob/8b5fc6c4d13a3dfd1d17a2007e2143b6da3447d7/Xamarin.Build.AsyncTask/AsyncTask.cs#L59