Allow overridding the exitPip destination bounds

Allows vendors to choose to restore to bounds other than the display
bounds on exit PIP. This is specially useful in freeform enabled
desktops where the previous windowing mode was freeform and PIP should
return to its original freeform bounds.

Bug: 225294296
Test: atest PinnedStackTests
Change-Id: Id25906c4b11e5f3c8351ba96cff80c63a6a5cf4e