RCTArrayBuffer zero-copy class for ObjC TM

[paradowstack]

Summary:

iOS TurboModules mapped a JS ArrayBuffer to NSData on arguments and NSMutableData on returns, so every crossing copied — and NSMutableData cannot alias foreign memory, so there was no way to express "these bytes live somewhere else".

This adds RCTArrayBuffer (packages/react-native/React/Base/) as the ObjC representation of an ArrayBuffer. It carries an isOwningBytes flag: an owning buffer can be stored and read from any thread, a non-owning one aliases bytes valid only for the synchronous call that produced it.

Codegen now emits RCTArrayBuffer * for ArrayBufferTypeAnnotation params (was NSData *) and returns (was NSMutableData *).

Changelog:

[IOS] [ADDED] - Add RCTArrayBuffer, the ObjC representation of a JS ArrayBuffer for TurboModules, with an explicit byte-ownership contract

Test Plan:

• RCTTurboModuleArrayBufferTests — 9 tests over the sync in-place path, isOwningBytes on a sync argument, returning one's own argument, the void/Promise copy paths, nesting, and a zero-length round trip.
• RCTTurboModuleTests.mm adds testNativeBackedArrayBufferIsAliasedAndKeepsBackingStoreAlive.
• RCTSampleTurboModule doubles its argument in place and returns the same buffer, covering the path end to end.
• Codegen and C++ API snapshots regenerated.

[meta-codesync]

@christophpurrer has imported this pull request. If you are a Meta employee, you can view this in D115629409.