[Xamarin.Android.Build.Tasks] remove @(_AndroidAssemblySkipCases) (#8622)

In an effort to remove old, unused code, we should be able to remove the
following related to the old `Android.Support.*` libraries:

* `Xamarin.Android.SkipCases.projitems` and the
  `@(_AndroidAssemblySkipCases)` item group.

This was a build performance optimization added in 02c07ed that would
*skip* a build step that normalized casing for `.dll` files with an
embedded `__AndroidLibraryProjects__.zip`. This optimization is not
needed at all for `.aar` files.

In .NET 9 projects, we don't create or embed
`__AndroidLibraryProjects__.zip`, so modern projects don't need this
optimization. Instead we bundle a `MyLibrary.aar` alongside
`MyLibrary.dll` inside of a `MyLibrary` NuGet package.

* Automatic trimming of the `Xamarin.Android.Support.*` assemblies

Modern packages mark themselves trimmable with `$(IsTrimmable)` or the
assembly-level attribute. Let's just remove the case for
`Android.Support` here.

Author: jonathanpeppers

build-tools/installers/create-installers.targets

@@ -157,7 +157,6 @@
     <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)Xamarin.Android.DesignTime.targets" />
     <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)Xamarin.Android.EmbeddedResource.targets" />
     <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)Xamarin.Android.Javac.targets" />
-    <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)Xamarin.Android.SkipCases.projitems" />
     <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)Xamarin.Android.Tooling.targets" />
     <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)Xamarin.Android.Tools.Aidl.dll" />
     <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)Xamarin.Android.Tools.Aidl.pdb" />

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

@@ -31,7 +31,7 @@ This file contains the .NET 5-specific targets to customize ILLink
           Trim="true" />
       <!-- TODO: remove setting the trim mode here, once the support packages are updated to NET6 and compatability packages not needed -->
       <ResolvedFileToPublish
-          Condition=" '$(AndroidLinkMode)' == 'SdkOnly' and ( $([System.String]::Copy(%(Filename)).StartsWith ('Xamarin.AndroidX.')) or $([System.String]::Copy(%(Filename)).StartsWith ('Xamarin.Android.Support.')) or $([System.String]::Copy(%(Filename)).StartsWith ('Xamarin.Google.')) or $([System.String]::Copy(%(Filename)).StartsWith ('Xamarin.GooglePlayServices.')) ) ">
+          Condition=" '$(AndroidLinkMode)' == 'SdkOnly' and ( $([System.String]::Copy(%(Filename)).StartsWith ('Xamarin.AndroidX.')) or $([System.String]::Copy(%(Filename)).StartsWith ('Xamarin.Google.')) or $([System.String]::Copy(%(Filename)).StartsWith ('Xamarin.GooglePlayServices.')) ) ">
         <TrimMode>link</TrimMode>
       </ResolvedFileToPublish>
 

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Build.Tasks.targets

@@ -149,9 +149,6 @@
     <None Include="Xamarin.Android.VisualBasic.targets">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </None>
-    <None Include="Xamarin.Android.SkipCases.projitems">
-      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-    </None>
   </ItemGroup>
   <ItemGroup>
     <None Include="ManifestOverlays\Timing.xml">

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets

@@ -376,7 +376,6 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
 <Import Project="$(MSBuildThisFileDirectory)Xamarin.Android.EmbeddedResource.targets" />
 <Import Project="$(MSBuildThisFileDirectory)Xamarin.Android.Javac.targets" />
 <Import Project="$(MSBuildThisFileDirectory)Xamarin.Android.Resource.Designer.targets" />
-<Import Project="$(MSBuildThisFileDirectory)Xamarin.Android.SkipCases.projitems" />
 <Import Project="$(MSBuildThisFileDirectory)Xamarin.Android.Tooling.targets" />
 
 <Target Name="_WriteLockFile" Condition=" '$(_AndroidDetectParallelBuilds)' == 'True' ">
@@ -401,10 +400,6 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
   />
 </Target>
 
-<ItemGroup>
-	<AndroidCustomMetaDataForReferences Include="@(_AndroidAssemblySkipCases)" />
-</ItemGroup>
-
 <Target Name="_AddAndroidCustomMetaData">
   <AppendCustomMetadataToItemGroup
       Condition="'$(AndroidApplication)' != '' And $(AndroidApplication)"