Distinguish exited pip task change

Shell only uses the windowing mode task info to decide whether the
task is entering pip.

But when entering pip or exiting pip, the task windowing mode is
pip and the activity windowing mode is fullscreen. The causes shell
to treat both cases as entering pip.

Bug: 353618234
Flag: EXEMPT bugfix
Test: Enable home rotation and auto rotation.
      Enter PiP in landscape.
      Leave PiP and rotate to portrait at the same time.
      The transition should be handled by DefaultTransitionHandler.
      And the PiP task should not be cropped by landscape bounds.
Change-Id: Ia3894d2a846dbd16d864e560d035ec1591fcb09c