[r8-obfuscation] Enable R8 JNI name obfuscation for NativeAOT

[simonrozsival]

Related to #12535

Depends on #12632

Layer 6 of 6 and the top of the replacement stack for draft PR #12575. Extends the shared two-pass R8 JNI name-obfuscation pipeline to NativeAOT, including incremental pre-ILC assembly rewriting, conservative JNI class/member reachability, seed-compatible final keep rules, and prebuilt runtime JNI startup keeps.

Testing:

• Modified target XML parses successfully.
• Xamarin.Android.Build.Tasks.csproj builds successfully.
• Complete Xamarin.Android.Build.Tests.csproj builds successfully.
• NativeAOT and direct-manifest generator tests: 28/28 passed.
• Cumulative focused R8/JNI unit suites: 165/165 passed.
• TypeMapAssemblyGeneratorTests: 121/121 passed, including owner-specific JNI method-name FieldRVA coverage.
• Independent Opus 5 correctness review found no remaining high-confidence issues and separately confirmed skipped incremental targets still evaluate item redirection.
• All three NativeAOT R8/JNI integration variants were attempted, but the local SDK stops before project code with NETSDK1147: To build this project, the following workloads must be installed: android; no unrelated workload was installed.

[simonrozsival]

/azp run

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[simonrozsival]

/azp run

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[simonrozsival]

/azp run

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[simonrozsival]

/azp run

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[MichalStrehovsky]

Why is this rewriting necessary? Can't we tell R8 not to rename things we need? There must be an escape hatch for reflection. What we're doing is reflection.

Bugs in rewritten assemblies pretty much always land on runtime team's plate to troubleshoot. dotnet/maui#37782 (comment) was the most recent one and that one was extra annoying because people who knew about the rewriting (they edited the rewriter files in the past) were on the thread and did not say there was a rewrite. I'm not a big fan of these approaches.

[simonrozsival]

@MichalStrehovsky we are looking into ways to support Google's new requirements on app optimizations (https://android-developers.googleblog.com/2026/08/app-quality-memory-optimization-secure-onboarding.html). We're currently using a -dontobfuscate flag, but it appears that that won't soon be acceptable by Play Store policy.

[jkotas]

@simonrozsival Michal's question was whether you can meet the requirement by generating fine-grained -keep directives in proguard-rules.pro file instead of IL rewriting. Have you evaluated that option? I agree that IL rewriting is always a factory for problems.

[jonathanpeppers]

I'm trying this out as an alternative, but we will have to submit an app to Google Play to test the full end-to-end:

• [r8] Obfuscate private Java members by default #12668