[TrimmableTypeMap] Trim value-type set instantiations

[simonrozsival]

Summary

• add a conditional external typemap universe for all 18 primitive and nullable Android.Runtime.JavaSet<T> instantiations
• keep the JavaSet universe, TypeMapping call, converter leaves, direct activation interception, and root discovery edge NativeAOT-only so they are fully trimmed from CoreCLR
• activate NativeAOT reference-type JavaSet<T> through a rooted JavaSet<IJavaPeerable> canonical template
• preserve CoreCLR concrete JavaSet<T> reflection and unsupported-value behavior
• keep ICollection<T> in the existing JavaCollection<T> universe because the target interface does not distinguish Java sets from other Java collections

Stack layer 4 above #12800. Base: simonrozsival-javacollection-typemap-universe at 54acba5784623ad6dbb30e62f7dc13b01b20bf1a. This PR contains only the JavaSet-specific delta. Stack metadata was not modified.

APK size

Identical unsigned Release android-arm64 MAUI APKs using the trimmable typemap. The previous layer is updated #12800; stack base is the exact main parent of #12793.

Runtime	Previous #12800	This PR	Change vs previous	Stack base	Change vs base
NativeAOT	13,372,429 B	13,376,698 B	+4,269 B (+0.032%)	14,180,177 B	-803,479 B (-5.666%)
CoreCLR	18,032,035 B	18,031,968 B	-67 B (-0.000%)	18,032,646 B	-678 B (-0.004%)

NativeAOT lib/arm64-v8a/libNativeAotSize.so uncompressed size: 21,471,016 B. The tiny CoreCLR byte variance is packaging noise; focused linked-output validation confirms the generated CoreCLR root has no dictionary/list/collection/set built-in edges and linked Mono.Android.dll has no value-type universe factory symbols.

Validation

• Microsoft.Android.Sdk.TrimmableTypeMap.Tests: 1,006 passed
• Microsoft.Android.Sdk.TrimmableTypeMap.IntegrationTests: 44 passed
• Mono.Android.csproj build: succeeded
• focused ReleaseTrimmableTypeMap_BuiltInCollectionUniversesAreNativeAotOnly: 2 passed (CoreCLR has zero built-in edges/symbols; NativeAOT retains all four)
• CoreCLR trimmable device category: 32 passed
• NativeAOT trimmable device category: 26 passed, 6 expected unsupported-reflection skips
• identical MAUI NativeAOT and CoreCLR publishes: succeeded