Account for animating children when updating task visibility

- It's possible for the root task to be hidden and not made visible
  again if only its children (ie. a leaf task) are animating

Bug: 218403080
Bug: 213603716
Test: atest NexusLauncherTests
Change-Id: I5f8b61afcbeff1974c8a60f62490afa602428219

services/core/java/com/android/server/wm/Task.java

@@ -3289,7 +3289,7 @@ class Task extends TaskFragment {
         // We intend to let organizer manage task visibility but it doesn't
         // have enough information until we finish shell transitions.
         // In the mean time we do an easy fix here.
-        final boolean show = isVisible() || isAnimating(TRANSITION | PARENTS);
+        final boolean show = isVisible() || isAnimating(TRANSITION | PARENTS | CHILDREN);
         if (mSurfaceControl != null) {
             if (show != mLastSurfaceShowing) {
                 getSyncTransaction().setVisibility(mSurfaceControl, show);