Add check for native animated node existing before starting animation

Summary:
We need to check that the animated node exists prior to executing the animation. The native animated node lifecycle is not synced with Fabric and nodes are frequently destroyed and re-created on rerenders. Therefore, there is a possibility that the the animated node does not exist when the native event is dispatched, in particular with native call batching.

Changelog:
[Internal] - Make NativeAnimatedNodesManager.getNodeById public

Reviewed By: JoshuaGross

Differential Revision: D37323138

fbshipit-source-id: ed0567871b4189c454b6b3145b853ecdfe844840

ReactAndroid/src/main/java/com/facebook/react/animated/NativeAnimatedNodesManager.java

@@ -100,8 +100,8 @@ public class NativeAnimatedNodesManager implements EventDispatcherListener {
     }
   }
 
-  /*package*/ @Nullable
-  AnimatedNode getNodeById(int id) {
+  @Nullable
+  public AnimatedNode getNodeById(int id) {
     return mAnimatedNodes.get(id);
   }