Access natively defined "nativeFabricUIManager" instead of importing it

Some places in the Fabric renderers access `nativeFabricUIManager` (a natively defined global) instead of importing UIManager. While this is coupling across repos that depends on the timing of events, it is necessary until we have a way to defer top-level imports to run after `nativeFabricUIManager` is defined. So for consistency we use `nativeFabricUIManager` everywhere (see the comment in #15604 (review) for more context).

Author: ide

packages/react-native-renderer/src/ReactFabricHostConfig.js

@@ -26,7 +26,6 @@ import {dispatchEvent} from './ReactFabricEventEmitter';
 
 // Modules provided by RN:
 import {
-  FabricUIManager,
   ReactNativeViewConfigRegistry,
   TextInputState,
   deepFreezeAndThrowOnMutationInDev,
@@ -46,7 +45,7 @@ const {
   measure: fabricMeasure,
   measureInWindow: fabricMeasureInWindow,
   measureLayout: fabricMeasureLayout,
-} = FabricUIManager;
+} = nativeFabricUIManager;
 
 const {get: getViewConfigForType} = ReactNativeViewConfigRegistry;
 

packages/react-native-renderer/src/__mocks__/react-native/Libraries/ReactPrivate/FabricUIManager.js renamed to packages/react-native-renderer/src/__mocks__/react-native/Libraries/ReactPrivate/InitializeNativeFabricUIManager.js

@@ -172,4 +172,4 @@ const RCTFabricUIManager = {
   }),
 };
 
-module.exports = RCTFabricUIManager;
+global.nativeFabricUIManager = RCTFabricUIManager;

packages/react-native-renderer/src/__mocks__/react-native/Libraries/ReactPrivate/ReactNativePrivateInterface.js

@@ -17,9 +17,6 @@ module.exports = {
   get Platform() {
     return require('./Platform');
   },
-  get FabricUIManager() {
-    return require('./FabricUIManager');
-  },
   get RCTEventEmitter() {
     return require('./RCTEventEmitter');
   },