change(android): make FabricUIManager#resolveView not thread specific

[hannojg]

Summary:

FabricUIManager#resolveView is not using any thread specific annotation, but has a UiThreadUtil.assertOnUiThread() check:

react-native/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/fabric/FabricUIManager.java

Lines 1034 to 1037 in d9262c6

	public @Nullable View resolveView(int reactTag) {
	UiThreadUtil.assertOnUiThread();
	SurfaceMountingManager surfaceManager = mMountingManager.getSurfaceManagerForView(reactTag);

However, after checking all data structures used, it appears that all of them are ConcurrentHashMaps and thus FabricUIManager#resolveView is actually thread safe:

react-native/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/fabric/FabricUIManager.java

Line 1038 in d93d325

return surfaceManager == null ? null : surfaceManager.getView(reactTag);

react-native/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/fabric/mounting/SurfaceMountingManager.java

Line 81 in d93d325

private ConcurrentHashMap<Integer, ViewState> mTagToViewState =

react-native/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/fabric/mounting/MountingManager.kt

Line 43 in d93d325

private val surfaceIdToManager = ConcurrentHashMap<Int, SurfaceMountingManager>() // any thread

I am proposing to remove the UiThreadUtil.assertOnUiThread() check here.

Motivation:

From another thread we want to check if a certain react tag is already mounted in the native view hierarchy. It should be the callers responsibility to make sure to only operate on that view from the UI thread.

Changelog:

[ANDROID] [CHANGED] Make FabricUIManager#resolveView not thread specific

Test Plan:

• Run the example app and make sure everything still works
• We tested this change and calling this method from another thread and it works without any weirdnesses