`CustomFabricUIManager` is accessing Fabric Internals

[cortinico]

Hey all,
Nicola from the React Native team here.

Just touching base because I noticed that CustomFabricUIManager is accessing Fabric Internals via reflection:

react-native-live-markdown/android/src/main/java/com/expensify/livemarkdown/CustomFabricUIManager.java

Lines 18 to 30 in 902f091

	Field mountingManagerField = uiManagerClass.getDeclaredField("mMountingManager");
	mountingManagerField.setAccessible(true);
	ReactApplicationContext reactContext = readPrivateField(source, "mReactApplicationContext");
	ViewManagerRegistry viewManagerRegistry = readPrivateField(source, "mViewManagerRegistry");
	BatchEventDispatchedListener batchEventDispatchedListener = readPrivateField(source, "mBatchEventDispatchedListener");
	MountingManager.MountItemExecutor mountItemExecutor = readPrivateField(source, "mMountItemExecutor");
	FabricUIManager customFabricUIManager = new FabricUIManager(reactContext, viewManagerRegistry, batchEventDispatchedListener);
	mountingManagerField.set(customFabricUIManager, new CustomMountingManager(viewManagerRegistry, mountItemExecutor, reactContext, markdownProps, parserId));
	return customFabricUIManager;

This is obviously not ideal an extremely brittle. I suspect this will break in 0.81 so I'm reaching out with ample time to make sure we find a workaround for this usage