Save reentry bounds from SysUI

On the other hand, since we won't be able to get the callback from
TaskOrganizer when an activity (used to be in PiP mode) is removed,
reset of the reentry bounds is kept in WM.

Bug: 152549281
Test: manually enter/exit PiP
Change-Id: I8b4b7f87c4a7601d8bdf32af8105a68450012a87