Fix view indices with Android LayoutAnimation

Summary:
Fixes issue #11828 that causes layout animations for removed views to
remove some adjacent views as well. This happens because the animated
views are still present in the ViewGroup, which throws off subsequent
operations that rely on view indices having updated.

This issue was addressed in #11962, which was closed in favour of a more
reliable solution that addresses the issue globally since it’s difficult
to account for animated views everywhere. janicduplessis [recommended][0]
handling the issue through ViewManager.

Since API 11, Android provides `ViewGroup#startViewTransition(View)`
that can be used to keep child views visible even if they have been
removed from the group. ViewGroup keeps an array of these views, which
is only used for drawing. Methods such as `ViewGroup#getChildCount()`
and `ViewGroup#getChildAt(int)` will ignore them.

I believe relying on these framework methods within ViewManager is the
most reliable way to solve this issue because it also works if callers
ignore ViewManager and reach into the native view indices and counts
directly.

[0]: #11962 (review)

I wrote a minimal test app that you can find here:

<https://gist.github.com/lnikkila/87f3825442a5773f17ead433a810d53f>

The expected result is that the red and green squares disappear, a blue
one appears, and the black one stays in place. iOS has this behaviour,
but Android removes the black square as well.

We can see the bug with some breakpoint logging.

Without LayoutAnimation:

```
    NativeViewHierarchyOptimizer: Removing node from parent with tag 2 at index 0
    NativeViewHierarchyOptimizer: Removing node from parent with tag 4 at index 1
    NativeViewHierarchyManager: Removing indices [0] with tags [2]
    RootViewManager: Removing child view at index 0 with tag 2
    NativeViewHierarchyManager: Removing indices [1] with tags [4]
    RootViewManager: Removing child view at index 1 with tag 4
```

With LayoutAnimation tag 3 gets removed when it shouldn’t be:

```
    NativeViewHierarchyOptimizer: Removing node from parent with tag 2 at index 0
    NativeViewHierarchyOptimizer: Removing node from parent with tag 4 at index 1
    NativeViewHierarchyManager: Removing indices [0] with tags [2]
    NativeViewHierarchyManager: Removing indices [1] with tags [4]
->  RootViewManager: Removing child view at index 1 with tag 3
    RootViewManager: Removing child view at index 2 with tag 4

    (Animation listener kicks in here)

    RootViewManager: Removing child view at index 1 with tag 2
```

Here are some GIFs to compare, click to expand:

<details>
  <summary><b>Current master (iOS vs Android)</b></summary>
  <p></p>
  <img src="https://user-images.githubusercontent.com/1291143/38695083-fbc29cd4-3e93-11e8-9150-9b8ea75b87aa.gif" height="400" /><img src="https://user-images.githubusercontent.com/1291143/38695108-06eb73a6-3e94-11e8-867a-b95d7f926ccd.gif" height="400" />
</details><p></p>

<details>
  <summary><b>With this patch (iOS vs Android, fixed)</b></summary>
  <p></p>
  <img src="https://user-images.githubusercontent.com/1291143/38695083-fbc29cd4-3e93-11e8-9150-9b8ea75b87aa.gif" height="400" /><img src="https://user-images.githubusercontent.com/1291143/38695137-1090f782-3e94-11e8-94c8-ce33a5d7ebdb.gif" height="400" />
</details><p></p>

Previously addressed in #11962, which wasn’t merged.

Tangentially related to my other LayoutAnimation PR #18651.

No documentation changes needed.

[ANDROID] [BUGFIX] [LayoutAnimation] - Removal LayoutAnimations no longer remove adjacent views as well in certain cases.
Closes #18830

Reviewed By: achen1

Differential Revision: D7612904

Pulled By: mdvacca

fbshipit-source-id: a04cf47ab80e0e813fa043125b1f907e212b1ad4

ReactAndroid/src/main/java/com/facebook/react/uimanager/NativeViewHierarchyManager.java

@@ -373,12 +373,13 @@ public synchronized void manageChildren(
         if (mLayoutAnimationEnabled &&
             mLayoutAnimator.shouldAnimateLayout(viewToRemove) &&
             arrayContains(tagsToDelete, viewToRemove.getId())) {
-          // The view will be removed and dropped by the 'delete' layout animation
-          // instead, so do nothing
-        } else {
-          viewManager.removeViewAt(viewToManage, indexToRemove);
+          // Display the view in the parent after removal for the duration of the layout animation,
+          // but pretend that it doesn't exist when calling other ViewGroup methods.
+          viewManager.startViewTransition(viewToManage, viewToRemove);
         }
 
+        viewManager.removeViewAt(viewToManage, indexToRemove);
+
         lastIndexToRemove = indexToRemove;
       }
     }
@@ -423,7 +424,9 @@ public synchronized void manageChildren(
           mLayoutAnimator.deleteView(viewToDestroy, new LayoutAnimationListener() {
             @Override
             public void onAnimationEnd() {
-              viewManager.removeView(viewToManage, viewToDestroy);
+              // Already removed from the ViewGroup, we can just end the transition here to
+              // release the child.
+              viewManager.endViewTransition(viewToManage, viewToDestroy);
               dropView(viewToDestroy);
             }
           });

ReactAndroid/src/main/java/com/facebook/react/uimanager/ViewGroupManager.java

@@ -93,6 +93,14 @@ public void removeAllViews(T parent) {
     }
   }
 
+  public void startViewTransition(T parent, View view) {
+    parent.startViewTransition(view);
+  }
+
+  public void endViewTransition(T parent, View view) {
+    parent.endViewTransition(view);
+  }
+
   /**
    * Returns whether this View type needs to handle laying out its own children instead of
    * deferring to the standard css-layout algorithm.