[TrimmableTypeMap] Don't stage shrunk assemblies into the shared runtime pack on NativeAOT

[simonrozsival]

Summary

For PublishTrimmed Android builds, _RemoveRegisterAttribute (in Xamarin.Android.Common.targets) copies every @(_ResolvedAssemblies) into its @(_ShrunkAssemblies) location. For the framework/user assemblies those shrunk destinations live inside the shared NuGet runtime pack, e.g.:

.../microsoft.netcore.app.runtime.nativeaot.android-arm64/<ver>/runtimes/android-arm64/lib/net11.0/shrunk/System.Xml.ReaderWriter.dll

Because multiple test projects — and the parallel per-RID inner builds — all target those same shared files, they race and fail intermittently on a clean pack cache with:

error XACIC7028: System.IO.FileNotFoundException: Could not find file
'.../lib/net11.0/shrunk/System.Xml.ReaderWriter.dll'
  at Microsoft.Android.Build.Tasks.Files.CopyIfChanged(String, String)
  at Xamarin.Android.Tasks.CopyIfChanged.RunTask()

This surfaced as intermittent CI failures in CheckCodeBehindIsGenerated(NativeAOT) and CheckOldResourceDesignerWithWrongCasingIsRemoved(True,NativeAOT). It does not reproduce locally because shrunk/ files left over from previous builds mask the missing source.

Fixes #11776.

Fix

On NativeAOT the managed framework/user assemblies are compiled to a native shared library by ILC and are never packaged, so these shrunk copies are only ever used as incremental-build inputs — CollectAssemblyFilesToCompress (the only task that reads their content) is already gated to '$(_AndroidRuntime)' != 'NativeAOT'.

This PR overrides _RemoveRegisterAttribute in the trimmable typemap path to, for NativeAOT, redirect the shrunk copies to a project-local intermediate directory ($(MonoAndroidIntermediateAssemblyDir)shrunk\) instead of the shared runtime pack. They are still produced with CopyIfChanged, so the copies keep stable timestamps (only rewritten when content actually changes), which preserves the @(_ShrunkAssemblies)/@(_ShrunkFrameworkAssemblies) incremental up-to-date checks — while nothing is ever written into the shared pack.

CoreCLR (and any other trimmable runtime) keeps the base behavior because it still packages the managed assemblies and therefore needs the shrunk copies in place.

Risk

Low and well-scoped:

• Only the '$(_AndroidRuntime)' == 'NativeAOT' branch changes behavior; CoreCLR-trimmable replicates the base target exactly.
• No effect on the default managed/MonoVM/CoreCLR paths.

Testing

Verified locally (both runtimes) that CheckCodeBehindIsGenerated, CheckOldResourceDesignerWithWrongCasingIsRemoved, and CSProjUserFileChanges (incremental) pass, and that the runtime pack's shrunk/ directory is no longer written for NativeAOT builds. Validated on CI in the context of the larger trimmable-typemap work (the two failing tests turned green and stayed green).

Sliced out of #11617 for focused review.

[Copilot]

Pull request overview

This PR prevents PublishTrimmed NativeAOT builds in the trimmable typemap path from copying “shrunk” assemblies into the shared runtime pack (NuGet cache), which can cause cross-project/per-RID parallel build races and intermittent XACIC7028 failures. It does so by overriding _RemoveRegisterAttribute to redirect the “shrunk” copy destinations into a project-local intermediate directory for NativeAOT, while keeping the existing behavior for CoreCLR/trimmable runtimes that still package managed assemblies.

Changes:

• Add an override of _RemoveRegisterAttribute in the trimmable typemap targets.
• For '$(_AndroidRuntime)' == 'NativeAOT', rewrite @(_ShrunkAssemblies) / @(_ShrunkFrameworkAssemblies) / @(_ShrunkUserAssemblies) to point under $(MonoAndroidIntermediateAssemblyDir)shrunk\... instead of the shared runtime pack.
• Preserve the existing copy behavior (CopyIfChanged) for non-NativeAOT trimmable runtimes.

Show a summary per file

File	Description
src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.TypeMap.Trimmable.targets	Overrides _RemoveRegisterAttribute to redirect shrunk assembly staging to a project-local intermediate path for NativeAOT, avoiding writes into shared runtime packs.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 0