[Xamarin.Android.Build.Tasks] Remove R8 assembly rewriter

[simonrozsival]

Summary

Remove the experimental build-time managed-assembly rewriting approach for R8 so any future assembly-rewriting design can start from a clean foundation.

This cleanup is related to #12535 and the original prototype in #12575.

What this PR undoes

This removes the managed rewriting implementation developed across the R8 obfuscation stack:

• [r8-obfuscation] Add PE metadata rebuild substrate #12629 added the PE metadata rebuild substrate.
• [r8-obfuscation] Rewrite managed JNI metadata from R8 mappings #12630 added managed JNI metadata rewriting from R8 mappings.
• [r8-obfuscation] Rewrite trimmable typemap JNI metadata #12631 added rewriting for generated trimmable type-map assemblies.
• [r8-obfuscation] Enable R8 JNI name obfuscation for CoreCLR #12632 and [r8-obfuscation] Enable R8 JNI name obfuscation for NativeAOT #12634 integrated and tested that rewriting approach for CoreCLR and NativeAOT.

Concretely, this PR removes the rewrite task, rewrite-only metadata/IL utilities, dedicated tests and fixtures, and the XA4325/XA4326 resources and documentation. The intent is to abandon this implementation rather than preserve an unused rewriting stack that a future design would need to work around.

What remains in place

• The generic R8Mapping parser introduced in [r8-obfuscation] Add R8 JNI mapping primitives #12628 remains, along with its tests and the MSBuildDeviceIntegration consumer. It is independently useful for reading R8 mapping files.
• The ordinary R8 configuration and private-members obfuscation/optimization policy from [r8] Add configurable private-member obfuscation and optimization #12668 remain unchanged. This PR does not disable R8 or remove private-member obfuscation.
• Existing D8/R8 packaging, ProGuard rule handling, and non-rewriting build behavior remain unchanged.
• Runtime remapping remains active as the stacked follow-up work in [runtime] Extend JNI remapping support #12847, [Xamarin.Android.Build.Tasks] Generate R8 JNI remapping tables #12848, [Xamarin.Android.Build.Tasks] Wire opt-in R8 runtime remapping #12692, and [Microsoft.Android.Build.Tasks] Move R8 remapping task to modern assembly #12844. Those PRs implement the alternative opt-in strategy without managed assembly rewriting and are not part of this cleanup diff.

We may revisit managed assembly rewriting in .NET 12 based on customer feedback and performance data, but with a fresh design rather than this implementation.

Validation

• Built Xamarin.Android.Build.Tasks
• Ran Microsoft.Android.Build.Tasks.Tests
• Ran Microsoft.Android.Sdk.TrimmableTypeMap.IntegrationTests
• Built MSBuildDeviceIntegration
• Ran focused R8MappingTests

[Copilot]

Copilot review overview

🟡 Changes recommended

The test project has an unresolved compile issue after the project reference removal; localization artifacts also need synchronization.

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Review effort: Lite
Findings: 1 · 1

Open (2)

• Remove stale Xamarin.Android.Tasks using after reference removal · New
• Synchronize localization artifacts after removing obsolete diagnostic keys · New

What changed in this PR

Removes the experimental R8 managed-assembly rewriter while retaining ordinary R8 processing and R8Mapping.

Changes:

• Deletes rewriter implementation, tasks, fixtures, and tests.
• Removes XA4325/XA4326 resources and documentation.
• Retains and updates R8Mapping tests.

File	Change
tests/​Microsoft.Android.Sdk.TrimmableTypeMap.IntegrationTests/​JniAssemblyRewriterTests.cs	Removes rewriter integration tests.
tests/​Microsoft.Android.Sdk.TrimmableTypeMap.IntegrationTests/​GeneratedTypeMapRewriterTests.cs	Removes typemap rewriter tests.
src/​Xamarin.Android.Build.Tasks/​Utilities/​JniRemapping/​NativeResourceSectionCopier.cs	Removes resource rewrite helper.
src/​Xamarin.Android.Build.Tasks/​Utilities/​JniRemapping/​MetadataRawColumns.cs	Removes metadata helper.
src/​Xamarin.Android.Build.Tasks/​Utilities/​JniRemapping/​MetadataEncoding.cs	Removes encoding helper.
src/​Xamarin.Android.Build.Tasks/​Utilities/​JniRemapping/​LdstrRewriter.cs	Removes string rewriter.
src/​Xamarin.Android.Build.Tasks/​Utilities/​JniRemapping/​JniRewritePlanner.cs	Removes rewrite planning logic.
src/​Xamarin.Android.Build.Tasks/​Utilities/​JniRemapping/​JniRewritePlan.cs	Removes rewrite plan and IL scanner.
src/​Xamarin.Android.Build.Tasks/​Utilities/​JniRemapping/​JniRewriteException.cs	Removes rewrite exception.
src/​Xamarin.Android.Build.Tasks/​Utilities/​JniRemapping/​JniDescriptorText.cs	Removes descriptor helper.
src/​Xamarin.Android.Build.Tasks/​Utilities/​JniRemapping/​JniAssemblyRewriter.cs	Removes rewriter entry point.
src/​Xamarin.Android.Build.Tasks/​Utilities/​JniRemapping/​IlOpcodeTable.cs	Removes opcode metadata.
src/​Xamarin.Android.Build.Tasks/​Utilities/​JniRemapping/​FieldRvaTable.cs	Removes FieldRVA support.
src/​Xamarin.Android.Build.Tasks/​Utilities/​JniRemapping/​CustomAttributeStringRewriter.cs	Removes attribute rewriting helper.
src/​Xamarin.Android.Build.Tasks/​Utilities/​JniRemapping/​AssemblyRebuilder.cs	Removes PE reconstruction implementation.
src/​Xamarin.Android.Build.Tasks/​Tests/​Xamarin.Android.Build.Tests/​Utilities/​JniRemapping/​R8MappingTests.cs	Retains parser coverage and removes deleted helper usage.
src/​Xamarin.Android.Build.Tasks/​Tests/​Xamarin.Android.Build.Tests/​Utilities/​JniRemapping/​NativeResourceSectionCopierTests.cs	Removes helper tests.
src/​Xamarin.Android.Build.Tasks/​Tests/​Xamarin.Android.Build.Tests/​Utilities/​JniRemapping/​LdstrRewriterTests.cs	Removes string-rewriter tests.
src/​Xamarin.Android.Build.Tasks/​Tests/​Xamarin.Android.Build.Tests/​Utilities/​JniRemapping/​JniFixtureBuilder.cs	Removes rewrite fixtures.
src/​Xamarin.Android.Build.Tasks/​Tests/​Xamarin.Android.Build.Tests/​Utilities/​JniRemapping/​JniDescriptorTextTests.cs	Removes descriptor-helper tests.
src/​Xamarin.Android.Build.Tasks/​Tests/​Xamarin.Android.Build.Tests/​Utilities/​JniRemapping/​AssemblyRebuilderTests.cs	Removes rebuilder tests.
src/​Xamarin.Android.Build.Tasks/​Tests/​Xamarin.Android.Build.Tests/​Tasks/​RewriteJniNamesForR8Tests.cs	Removes task tests.
src/​Xamarin.Android.Build.Tasks/​Tasks/​RewriteJniNamesForR8.cs	Removes the experimental rewrite task.
src/​Xamarin.Android.Build.Tasks/​Properties/​Resources.resx	Removes XA4325/XA4326 resources.
src/​Xamarin.Android.Build.Tasks/​Properties/​Resources.Designer.cs	Removes generated resource accessors.
src/​Microsoft.Android.Build.Tasks/​Tests/​Microsoft.Android.Build.Tasks.Tests/​Microsoft.Android.Build.Tasks.Tests.csproj	Removes the rewriter-only project reference.
src/​Microsoft.Android.Build.Tasks/​Tests/​Microsoft.Android.Build.Tasks.Tests/​JniAssemblyRewriterTypeMapTests.cs	Removes rewriter type-map tests.
Documentation/​docs-mobile/​TOC.yml	Removes diagnostic navigation entries.
Documentation/​docs-mobile/​messages/​xa4326.md	Removes XA4326 documentation.
Documentation/​docs-mobile/​messages/​xa4325.md	Removes XA4325 documentation.
Documentation/​docs-mobile/​messages/​index.md	Removes diagnostic index entries.

Files not reviewed (1)

• src/Xamarin.Android.Build.Tasks/Properties/Resources.Designer.cs: Generated file