Fix not callback onTaskMovedToFront when dismissing split

After I5dac8826e, launcher relies on onTaskMovedToFront to track the top
most task. But in wm-core, it doesn't invoke onTaskMovedToFront when
reparenting a leaf task to TaskDisplayArea, like when dismissing split
screen. This makes sure to cover such flow.

Fix: 229828519
Test: dismiss focused split side, enter overview, observed app icon is
      correct.
Change-Id: Iaf420c8c7d80d3c80b2eeca31cad8718e541d8a1

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

@@ -5997,6 +5997,9 @@ class Task extends TaskFragment {
 
         if (canBeLaunchedOnDisplay(newParent.getDisplayId())) {
             reparent(newParent, onTop ? POSITION_TOP : POSITION_BOTTOM);
+            if (isLeafTask()) {
+                newParent.onLeafTaskMoved(this, onTop);
+            }
         } else {
             Slog.w(TAG, "Task=" + this + " can't reparent to " + newParent);
         }