[Xamarin.Android.Build.Tasks] Use marshal-ilgen component

Fixes: dotnet#7249

Context: dotnet/runtime#71203
Context: dotnet/runtime#60639
Context: dotnet/runtime#61685

Mono introduced a new `marshal-ilgen` component in
dotnet/runtime@de32c446 which needs to be used when
*non-blittable type* is required.

`string` marshaling is a form of non-blittable marshaling.

Eventually the idea is that assemblies should migrate to use the
[`DllImport Generator`][0] for non-blittable marshaling purposes,
then [`[assembly:DisableRuntimeMarshallingAttribute]`][1] can be
applied to the assembly, and -- if no assemblies in an Android app
require non-blittable marshaling -- then the `marshal-ilgen`
component can be omitted from the `.apk`, reducing app size.

That's a fair number of `if`s; this won't be happening soon.

In the meantime, we need to start including the `marshal-ilgen`
component in all .NET 7 RC1+ builds so that our existing `DllImport`
declarations continue to work.

Update `@(_MonoComponent)` to add `marshal-ilgen`.

In order to facilitate future testing, allow the `marshal-ilgen`
component to be *excluded* if the
`$(_AndroidExcludeMarshalIlgenComponent)` property is True.

[0]: https://github.com/dotnet/runtimelab/tree/feature/DllImportGenerator
[1]: dotnet/runtime#60639

Author: jonpryor

src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.AssemblyResolution.targets

@@ -198,6 +198,7 @@ _ResolveAssemblies MSBuild target.
       <_MonoComponent Condition=" '$(AndroidEnableProfiler)' == 'true' " Include="diagnostics_tracing" />
       <_MonoComponent Condition=" '$(AndroidUseInterpreter)' == 'true' " Include="hot_reload" />
       <_MonoComponent Condition=" '$(AndroidIncludeDebugSymbols)' == 'true' " Include="debugger" />
+      <_MonoComponent Condition=" '$(_AndroidExcludeMarshalIlgenComponent)' != 'true' " Include="marshal-ilgen" />
     </ItemGroup>
     <ProcessNativeLibraries
         InputLibraries="@(_ResolvedNativeLibraries)"