[xabt] Move StripEmbeddedLibraries trimmer step to MSBuild task (#10894)

Move embedded resource stripping out of the ILLink custom step so it
runs after ILLink but before ReadyToRun/crossgen2 in the inner build,
ensuring R2R images are generated from already-stripped assemblies.

- Trimmed builds: new StripEmbeddedLibraries MSBuild task runs via
  _StripEmbeddedLibraries target (AfterTargets="ILLink") in the inner
  build, processing assemblies in-place with temp-write-copy-back.
- Non-trimmed builds: new StripEmbeddedLibrariesStep added to
  LinkAssembliesNoShrink pipeline.
- Shared ShouldStripResource() logic between both paths.
- Removed old _TrimmerCustomSteps registration and deleted the ILLink
  StripEmbeddedLibraries.cs (now dead code).

Co-authored-by: Jonathan Peppers <jonathan.peppers@microsoft.com>

Author: sbomer

src/Microsoft.Android.Sdk.ILLink/StripEmbeddedLibraries.cs

@@ -7,6 +7,7 @@
   <UsingTask TaskName="Xamarin.Android.Tasks.GetMonoPlatformJar" AssemblyFile="$(_XamarinAndroidBuildTasksAssembly)" />
   <UsingTask TaskName="Xamarin.Android.Tasks.RemoveRegisterAttribute" AssemblyFile="$(_XamarinAndroidBuildTasksAssembly)" />
   <UsingTask TaskName="Xamarin.Android.Tasks.GenerateProguardConfiguration" AssemblyFile="$(_XamarinAndroidBuildTasksAssembly)" />
+  <UsingTask TaskName="Xamarin.Android.Tasks.StripEmbeddedLibraries" AssemblyFile="$(_XamarinAndroidBuildTasksAssembly)" />
 
   <PropertyGroup>
     <_RemoveRegisterFlag>$(MonoAndroidIntermediateAssemblyDir)shrunk\shrunk.flag</_RemoveRegisterFlag>
@@ -203,7 +204,6 @@
           Type="MonoDroid.Tuner.AddKeepAlivesStep"
       />
       <!-- Custom steps that run after CleanStep -->
-      <_TrimmerCustomSteps Include="$(_AndroidLinkerCustomStepAssembly)" AfterStep="CleanStep" Type="MonoDroid.Tuner.StripEmbeddedLibraries" />
       <_TrimmerCustomSteps
           Condition=" '$(AndroidLinkResources)' == 'true' "
           Include="$(_AndroidLinkerCustomStepAssembly)"
@@ -250,6 +250,22 @@
     <Touch Files="$(_AndroidLinkFlag)" AlwaysCreate="true" />
   </Target>
 
+  <!--
+    Strip embedded Android resources (.jar, native libs, etc.) from trimmed assemblies.
+    Runs in the inner build after ILLink but before ReadyToRun/crossgen2 compilation,
+    so R2R images are generated from already-stripped assemblies.
+  -->
+  <Target Name="_StripEmbeddedLibraries"
+      AfterTargets="ILLink"
+      Condition=" '$(PublishTrimmed)' == 'true' ">
+    <ItemGroup>
+      <_StripEmbeddedLibrariesAssembly Include="@(ResolvedFileToPublish)" Condition=" '%(Extension)' == '.dll' " />
+    </ItemGroup>
+    <StripEmbeddedLibraries
+        Assemblies="@(_StripEmbeddedLibrariesAssembly)"
+        Deterministic="$(Deterministic)" />
+  </Target>
+
   <!-- Inject _TypeMapKind into the property cache -->
   <Target Name="_SetTypemapProperties"
       BeforeTargets="_CreatePropertiesCache">

src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.TypeMap.LlvmIr.targets

@@ -0,0 +1,116 @@
+#nullable enable
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using Microsoft.Android.Build.Tasks;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+using Mono.Cecil;
+
+namespace Xamarin.Android.Tasks;
+
+/// <summary>
+/// An MSBuild task that strips embedded Android resources (.jar, __AndroidNativeLibraries__.zip,
+/// __AndroidLibraryProjects__.zip, __AndroidEnvironment__) from trimmed assemblies.
+///
+/// This runs in the inner build after ILLink but before ReadyToRun/crossgen2 compilation,
+/// so that R2R images are generated from the already-stripped assemblies.
+/// </summary>
+public class StripEmbeddedLibraries : AndroidTask
+{
+	public override string TaskPrefix => "SEL";
+
+	[Required]
+	public ITaskItem [] Assemblies { get; set; } = [];
+
+	public bool Deterministic { get; set; }
+
+	public override bool RunTask ()
+	{
+		var resolver = new DefaultAssemblyResolver ();
+		var searchDirectories = new HashSet<string> (StringComparer.OrdinalIgnoreCase);
+
+		foreach (var assembly in Assemblies) {
+			var dir = Path.GetFullPath (Path.GetDirectoryName (assembly.ItemSpec) ?? "");
+			if (searchDirectories.Add (dir)) {
+				resolver.AddSearchDirectory (dir);
+			}
+		}
+
+		try {
+			foreach (var assembly in Assemblies) {
+				if (MonoAndroidHelper.IsFrameworkAssembly (assembly)) {
+					continue;
+				}
+
+				StripAssembly (assembly.ItemSpec, resolver);
+			}
+		} finally {
+			resolver.Dispose ();
+		}
+
+		return !Log.HasLoggedErrors;
+	}
+
+	void StripAssembly (string assemblyPath, IAssemblyResolver resolver)
+	{
+		string pdbPath = Path.ChangeExtension (assemblyPath, ".pdb");
+		bool havePdb = File.Exists (pdbPath);
+
+		var readerParams = new ReaderParameters {
+			ReadSymbols = havePdb,
+			ReadWrite = true,
+			AssemblyResolver = resolver,
+		};
+
+		bool assembly_modified = false;
+
+		using (var assembly = AssemblyDefinition.ReadAssembly (assemblyPath, readerParams)) {
+			foreach (var module in assembly.Modules) {
+				foreach (var resource in module.Resources.ToArray ()) {
+					if (ShouldStripResource (resource)) {
+						Log.LogDebugMessage ($"  Stripped {resource.Name} from {assembly.Name.Name}.dll");
+						module.Resources.Remove (resource);
+						assembly_modified = true;
+					}
+				}
+			}
+
+			if (!assembly_modified) {
+				return;
+			}
+
+			Log.LogDebugMessage ($"  Writing stripped assembly: {assemblyPath}");
+			assembly.Write (new WriterParameters {
+				WriteSymbols = havePdb,
+				DeterministicMvid = Deterministic,
+			});
+		}
+	}
+
+	/// <summary>
+	/// Determines whether a resource should be stripped from the assembly.
+	/// Matches the same criteria as the old ILLink StripEmbeddedLibraries step.
+	/// </summary>
+	internal static bool ShouldStripResource (Resource resource)
+	{
+		if (!(resource is EmbeddedResource))
+			return false;
+		// Embedded jars
+		if (resource.Name.EndsWith (".jar", StringComparison.InvariantCultureIgnoreCase))
+			return true;
+		// Embedded AndroidNativeLibrary archive
+		if (resource.Name == "__AndroidNativeLibraries__.zip")
+			return true;
+		// Embedded AndroidResourceLibrary archive
+		if (resource.Name == "__AndroidLibraryProjects__.zip")
+			return true;
+		// Embedded AndroidEnvironment items
+		if (resource.Name.StartsWith ("__AndroidEnvironment__", StringComparison.Ordinal))
+			return true;
+		return false;
+	}
+
+}