Expose getEventDispatcher() method into UIManager interface

Summary:
This diff promotes the UIManagerModule.getEventDispatcher() to the interface UIManager and it implements this method in FabricUIManager class.

Changelog: [internal]

Reviewed By: JoshuaGross

Differential Revision: D18862862

fbshipit-source-id: 424f0e601ed1807dbd5d33048daf7dc3bb200dcd

ReactAndroid/src/main/java/com/facebook/react/bridge/UIManager.java

@@ -56,6 +56,9 @@ public interface UIManager extends JSIModule, PerformanceCounter {
    */
   void dispatchCommand(int reactTag, String commandId, @Nullable ReadableArray commandArgs);
 
+  /** @return the {@link EventDispatcher} object that is used by this class. */
+  <T> T getEventDispatcher();
+
   /**
    * Used by native animated module to bypass the process of updating the values through the shadow
    * view hierarchy. This method will directly update native views, which means that updates for

ReactAndroid/src/main/java/com/facebook/react/fabric/FabricUIManager.java

@@ -693,6 +693,13 @@ public class FabricUIManager implements UIManager, LifecycleEventListener {
         .postFrameCallback(ReactChoreographer.CallbackType.DISPATCH_UI, mDispatchUIFrameCallback);
   }
 
+  @Override
+  @NonNull
+  @SuppressWarnings("unchecked")
+  public EventDispatcher getEventDispatcher() {
+    return mEventDispatcher;
+  }
+
   @Override
   public void onHostPause() {
     ReactChoreographer.getInstance()