Prevent ZBoost of TaskDisplayArea

Before, when an activity needs z boost, the whole TDA is moved above
other windows of ABOVE_TASKS. Now, we don't move TDA anymore.

Fix: 149651594
Test: manual: open app and expand notification before app fully start,
the app no longer moves above notification.
Test: atest WmTests:TaskDisplayAreaTests#testActivityWithZBoost_TaskDisplayAreaDoesNotMovedUp

Change-Id: Ie1eae7a5566fc8988cd3ca9f4a56332743facf52