Fix possible ConcurrentModificationException when accessing the lis…

…t of view managers (#35770)

Summary:
With the current implementation, it's possible to get a reference to the list of view managers while it's being populated, which in some cases results in `ConcurrentModificationException` thrown [here](https://github.com/facebook/react-native/blob/9c57a7f20925765da69590256ca8755b71735cdb/ReactAndroid/src/main/java/com/facebook/react/uimanager/UIManagerModuleConstantsHelper.java#L80). This PR updates the logic, so the reference to the list is updated (and returned) only when it's ready.

## Changelog

[ANDROID] [FIXED] - Fix possible `ConcurrentModificationException` in `UIManagerModuleConstantsHelper::createConstants`

Pull Request resolved: #35770

Reviewed By: cortinico

Differential Revision: D42342107

Pulled By: rshest

fbshipit-source-id: 8d799535c811edeefa1903fbf7a46bff22691e59

ReactAndroid/src/main/java/com/facebook/react/ReactInstanceManager.java

@@ -923,10 +923,11 @@ public List<ViewManager> getOrCreateViewManagers(
       if (mViewManagers == null) {
         synchronized (mPackages) {
           if (mViewManagers == null) {
-            mViewManagers = new ArrayList<>();
+            ArrayList<ViewManager> viewManagers = new ArrayList<>();
             for (ReactPackage reactPackage : mPackages) {
-              mViewManagers.addAll(reactPackage.createViewManagers(catalystApplicationContext));
+              viewManagers.addAll(reactPackage.createViewManagers(catalystApplicationContext));
             }
+            mViewManagers = viewManagers;
             return mViewManagers;
           }
         }