Avoid start/finishOperationBatch when using singleOp Animated experiment

Summary:
Splitting these changes of from D36482630, which is a minor improvement to the singleOp experiment. Since we call start/finish already on the native side, we don't need to repeat it from JS.

Changelog: [Internal]

Reviewed By: JoshuaGross

Differential Revision: D36541700

fbshipit-source-id: 7d61669710faca3153be557fb2d214011eda87c5

Author: javache

Libraries/Animated/NativeAnimatedHelper.js

@@ -150,9 +150,6 @@ const API = {
     invariant(NativeAnimatedModule, 'Native animated module is not available');
     flushQueueTimeout = null;
 
-    if (Platform.OS === 'android') {
-      NativeAnimatedModule.startOperationBatch?.();
-    }
     if (useSingleOpBatching) {
       // Set up event listener for callbacks if it's not set up
       if (
@@ -168,13 +165,13 @@ const API = {
       NativeAnimatedModule.queueAndExecuteBatchedOperations?.(singleOpQueue);
       singleOpQueue.length = 0;
     } else {
+      Platform.OS === 'android' && NativeAnimatedModule.startOperationBatch?.();
       for (let q = 0, l = queue.length; q < l; q++) {
         queue[q]();
       }
       queue.length = 0;
-    }
-    if (Platform.OS === 'android') {
-      NativeAnimatedModule.finishOperationBatch?.();
+      Platform.OS === 'android' &&
+        NativeAnimatedModule.finishOperationBatch?.();
     }
   },
   queueOperation: <Args: $ReadOnlyArray<mixed>, Fn: (...Args) => void>(

ReactAndroid/src/main/java/com/facebook/react/fabric/mounting/MountItemDispatcher.java

@@ -126,6 +126,8 @@ public boolean tryDispatchMountItems() {
       mInDispatch = false;
     }
 
+    // We call didDispatchMountItems regardless of whether we actually dispatched anything, since
+    // NativeAnimatedModule relies on this for executing any animations that may have been scheduled
     mItemDispatchListener.didDispatchMountItems();
 
     // Decide if we want to try reentering