Use MutableIntObjectMap for SurfaceMountingManager view registry (#56646)

[javache]

Summary:

Replace ConcurrentHashMap<Int, ViewState> with MutableIntObjectMap<ViewState> + ReentrantReadWriteLock in SurfaceMountingManager, behind the useOptimizedViewRegistryOnAndroid feature flag.

ConcurrentHashMap<Int, ViewState> boxes every Int key to java.lang.Integer (16 bytes) and allocates a Node object per entry (~32 bytes). MutableIntObjectMap from androidx.collection uses a Swiss Table layout with primitive IntArray keys — ~9 bytes/entry vs ~56-64 bytes, a ~6x reduction in map overhead. For a complex surface with 2000+ views, this saves ~90KB per surface in map overhead alone, plus reduced GC pressure from eliminating Integer boxing.

The ReentrantReadWriteLock replaces CHM's built-in concurrency. This matches the access pattern: reads from any thread (getEventEmitter, enqueuePendingEvent), writes almost exclusively from the UI thread. Readers never block each other. stopSurface snapshots entries under the write lock and processes onViewStateDeleted outside the lock to minimize reader blocking.

Changelog: [Internal]

Reviewed By: sammy-SC

Differential Revision: D102797904

[meta-codesync]

@javache has exported this pull request. If you are a Meta employee, you can view the originating Diff in D102797904.

[meta-codesync]

This pull request has been merged in 06b23b8.

[react-native-bot]

This pull request was successfully merged by @javache in 06b23b8

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