Android: preserve fbjni internals in minified apps

[cdeil]

Summary

• preserve fbjni classes and members according to fbjni's own @DoNotStrip and @DoNotStripAny annotations
• scope the rules to com.facebook.jni.** so they do not affect unrelated annotated dependencies
• suppress the warning for fbjni's compile-time-only javax.annotation.Nullable reference

This is a follow-up to #19169. That PR protects ExecuTorch's annotated classes, but a minified consumer can still remove fbjni internals that ExecuTorch's native bindings need.

Motivation

In a standalone release app with R8 enabled, both the 1.4.0 Maven AAR and the 1.4.1 release AAR abort in Module.initHybrid() with SIGABRT and abort message ptr. The R8 mapping contains com.facebook.jni.HybridData, but not its annotated HybridData$Destructor class.

Keeping all org.pytorch.executorch.** classes is not sufficient. Applying the scoped fbjni annotation rules preserves HybridData$Destructor and lets the same model execute successfully.

Test plan

Standalone Android consumer using AGP 9.1.1, Gradle 9.5, minifyEnabled = true, and a one-element add-one PTE model on an arm64 Android tablet:

AAR	Stock consumer rules	With this patch
1.4.0	aborts in Module.initHybrid()	PASS: output=2.0
1.4.1	aborts in Module.initHybrid()	PASS: output=2.0

The unminified build passes as a control. The fixed R8 mapping retains com.facebook.jni.HybridData$Destructor; the stock mapping does not.

The current Android project builds the AAR but does not contain a minified standalone consumer target, so this red/green test was run in a separate minimal consumer app.

• git diff --check origin/main...HEAD

[pytorch-bot]

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[cdeil]

@pytorchbot label "release notes: build"

[Copilot]

Pull request overview

This PR updates the ExecuTorch Android AAR’s consumer R8/ProGuard configuration to prevent minified consumer apps from stripping fbjni internals that ExecuTorch’s JNI bindings rely on at runtime.

Changes:

• Add scoped keep rules for com.facebook.jni.** based on fbjni’s @DoNotStrip / @DoNotStripAny annotations.
• Suppress R8 warnings for fbjni’s compile-time-only javax.annotation.Nullable reference.

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[Copilot]

Pull request overview

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