[TrimmableTypeMap] Preserve trimmable typemap outputs on no-op builds

[simonrozsival]

Summary

• replay generated trimmable typemap assemblies and Java outputs into FileWrites before IncrementalClean
• keep generated typemap DLL metadata stable for packaging/native config consumers
• extend the trimmable typemap incremental test to assert generated DLLs survive a no-op rebuild

Related to #10958.

Relevant sub-issues:

• Related to [TrimmableTypeMap] Fix stale per-assembly typemap output invalidation #11489: fixes one incremental-output preservation case, but does not fully address stale per-assembly typemap invalidation from non-assembly input changes.
• Context for [TrimmableTypeMap] Add ComputeTypeMapDependencies pre-task for partial builds #11492 and [TrimmableTypeMap] Split Debug typemap generation into per-assembly MSBuild units #11494: dynamic typemap outputs must remain visible to MSBuild incremental clean before deeper partial-build/per-assembly target work.
• Tangentially related to [TrimmableTypeMap] Reconcile ACW map generation with per-assembly incrementality #11495: keeps acw-map.txt recorded in FileWrites, but does not split or merge ACW maps.

Validation

• ./dotnet-local.sh build src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Xamarin.Android.Build.Tests.csproj -c Debug -v:minimal -nr:false
• MSBUILDDISABLENODEREUSE=1 ./dotnet-local.sh test bin/TestDebug/net10.0/Xamarin.Android.Build.Tests.dll --filter "Name~Build_WithTrimmableTypeMap_IncrementalBuild" -v:minimal (skipped locally because commercial build targets are unavailable)

[Copilot]

Pull request overview

This PR addresses a trimmable typemap incremental-build issue where MSBuild’s IncrementalClean could delete previously generated typemap DLLs / Java outputs on no-op builds (because skipped targets don’t re-populate @(FileWrites)). It replays the prior dynamic outputs into @(FileWrites) early in the build and strengthens the incremental test to ensure the generated typemap assemblies survive a no-op rebuild.

Changes:

• Add a _RecordTrimmableTypeMapFileWrites target that re-emits typemap-generated DLL/Java outputs into @(FileWrites) before _CleanGetCurrentAndPriorFileWrites runs.
• Refactor typemap assembly item construction via a dedicated @(_TrimmableTypeMapResolvedAssemblies) item list and then feed it into both @(_ResolvedAssemblies) and @(_ShrunkAssemblies).
• Extend Build_WithTrimmableTypeMap_IncrementalBuild to assert typemap DLLs from the first build still exist after a no-op second build.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/TrimmableTypeMapBuildTests.cs	Adds an assertion that typemap DLL outputs persist across a no-op rebuild where _GenerateJavaStubs is skipped.
src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.TypeMap.Trimmable.targets	Replays prior dynamic typemap outputs into @(FileWrites) before IncrementalClean and slightly restructures typemap DLL item population for packaging/native config.