Rename FabricMountItem.* to MountItem.* (#36722)

Summary:
Changelog: [Android] [Breaking] - Renamed FabricMountItem.* files to MountItem.* to better match the name of the struct.

Pull Request resolved: https://github.com/facebook/react-native/pull/36722

Reviewed By: cortinico, cipolleschi

Differential Revision: D44540079

fbshipit-source-id: 79d8aa7c6f6b908be52009c51c4ea2f601f788fd

packages/react-native/ReactAndroid/src/main/jni/react/fabric/FabricMountingManager.cpp

@@ -8,7 +8,7 @@
 #include "FabricMountingManager.h"
 
 #include "EventEmitterWrapper.h"
-#include "FabricMountItem.h"
+#include "MountItem.h"
 #include "StateWrapperImpl.h"
 
 #include <react/jni/ReadableNativeMap.h>

packages/react-native/ReactAndroid/src/main/jni/react/fabric/MountItem.cpp

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-#include "FabricMountItem.h"
+#include "MountItem.h"
 
 namespace facebook {
 namespace react {