Fixed native animated crash because of thread-safe issue (#24063)

Summary:
After we imported Fabric surface presenter observer mechanism, the thread-safe issue comes up, `operations` may read-write on main thread and shadow queue.

```
2019-03-20 15:53:21.249742+0800 RNTester[36039:1402802] *** Terminating app due to uncaught exception 'NSGenericException', reason: '*** Collection <__NSArrayM: 0x60000396a730> was mutated while being enumerated.'
*** First throw call stack:
(
    0   CoreFoundation                      0x00000001083221bb __exceptionPreprocess + 331
    1   libobjc.A.dylib                     0x0000000106a07735 objc_exception_throw + 48
    2   CoreFoundation                      0x000000010831ee9c __NSFastEnumerationMutationHandler + 124
    3   RNTester                            0x00000001048c8784 -[RCTNativeAnimatedModule didMountComponentsWithRootTag:] + 596
    4   RNTester                            0x000000010491423e -[RCTSurfacePresenter mountingManager:didMountComponentsWithRootTag:] + 1662
    5   RNTester                            0x00000001048f54e9 -[RCTMountingManager _performMountItems:rootTag:] + 1369
    6   RNTester                            0x00000001048f4eba __62-[RCTMountingManager performTransactionWithMutations:rootTag:]_block_invoke + 58
    7   RNTester                            0x0000000104710d1d __RCTExecuteOnMainQueue_block_invoke + 29
    8   libdispatch.dylib                   0x000000010a4db595 _dispatch_call_block_and_release + 12
    9   libdispatch.dylib                   0x000000010a4dc602 _dispatch_client_callout + 8
    10  libdispatch.dylib                   0x000000010a4e999a _dispatch_main_queue_callback_4CF + 1541
    11  CoreFoundation                      0x00000001082873e9 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
    12  CoreFoundation                      0x0000000108281a76 __CFRunLoopRun + 2342
    13  CoreFoundation                      0x0000000108280e11 CFRunLoopRunSpecific + 625
    14  GraphicsServices                    0x000000010e0c11dd GSEventRunModal + 62
    15  UIKitCore                           0x000000011567281d UIApplicationMain + 140
    16  RNTester                            0x0000000104553380 main + 112
    17  libdyld.dylib                       0x000000010a552575 start + 1
)

```

[iOS] [Fixed] - Fixed native animated crash because of thread-safe issue
Pull Request resolved: https://github.com/facebook/react-native/pull/24063

Differential Revision: D14563994

Pulled By: shergin

fbshipit-source-id: 98970c8993b7b794273ed3a8c40dbbce147e1f4b

Libraries/NativeAnimation/RCTNativeAnimatedModule.m

@@ -236,19 +236,27 @@ RCT_EXPORT_METHOD(removeAnimatedEventFromView:(nonnull NSNumber *)viewTag
 - (void)willMountComponentsWithRootTag:(NSInteger)rootTag
 {
   RCTAssertMainQueue();
-  for (AnimatedOperation operation in _preOperations) {
+  __block NSArray<AnimatedOperation> *preOperations;
+  RCTUnsafeExecuteOnUIManagerQueueSync(^{
+    preOperations = self->_preOperations;
+    self->_preOperations = [NSMutableArray new];
+  });
+  for (AnimatedOperation operation in preOperations) {
     operation(self->_nodesManager);
   }
-  _preOperations = [NSMutableArray new];
 }
 
 - (void)didMountComponentsWithRootTag:(NSInteger)rootTag
 {
   RCTAssertMainQueue();
-  for (AnimatedOperation operation in _operations) {
+  __block NSArray<AnimatedOperation> *operations;
+  RCTUnsafeExecuteOnUIManagerQueueSync(^{
+    operations = self->_operations;
+    self->_operations = [NSMutableArray new];
+  });
+  for (AnimatedOperation operation in operations) {
     operation(self->_nodesManager);
   }
-  _operations = [NSMutableArray new];
 }
 
 #pragma mark - RCTUIManagerObserver