Sync mLastLeafTaskToFrontId to moveTaskToFront callback.

When moving the task to the back and trying to update the new task
moving to the front, instead of invalidating the taskId, we should
update it to the one that's about to be moved to the front.

Bug: 408967675
Bug: 409160132
Test: Manual - Enter PiP while in Desktop mode (via minimize), close
PiP, swipe up to Overview to verify no UI issue
Flag: EXEMPT bug fix

Change-Id: I62ec04833989cc2d56dd67f271a58b958795293e