Add a hack to fix the Modal component interacting with LayoutAnimation

Summary: As per the comment, <Modal> uses entering/leaving the view hierarchy as a cue to show/hide the modal. By re-adding it, we are causing a bunch of confusion.

Reviewed By: shergin

Differential Revision: D5893607

fbshipit-source-id: ecd05799751a9bba843998ae93f24fe35edca8b4

React/Modules/RCTUIManager.m

@@ -784,11 +784,10 @@ - (void)_removeChildren:(NSArray<UIView *> *)children
     UIView *originalSuperview = removedChild.superview;
     NSUInteger originalIndex = [originalSuperview.subviews indexOfObjectIdenticalTo:removedChild];
     [container removeReactSubview:removedChild];
-    [originalSuperview insertSubview:removedChild atIndex:originalIndex];
-
     // Disable user interaction while the view is animating
     // since the view is (conseptually) deleted and not supposed to be interactive.
     removedChild.userInteractionEnabled = NO;
+    [originalSuperview insertSubview:removedChild atIndex:originalIndex];
 
     NSString *property = deletingLayoutAnimation.property;
     [deletingLayoutAnimation performAnimations:^{

React/Views/RCTModalHostView.m

@@ -160,6 +160,12 @@ - (void)didMoveToWindow
 {
   [super didMoveToWindow];
 
+  // In the case where there is a LayoutAnimation, we will be reinserted into the view hierarchy but only for aesthetic purposes.
+  // In such a case, we should NOT represent the <Modal>.
+  if (!self.userInteractionEnabled && ![self.superview.reactSubviews containsObject:self]) {
+    return;
+  }
+
   if (!_isPresented && self.window) {
     RCTAssert(self.reactViewController, @"Can't present modal view controller without a presenting view controller");