Implement window enter/exit animations as system level XML animations.

Note this generalizes from previous 'circle' presumptions and generalizes to 'rounded' windows. Implementation is largely unchanged as actual radius will be determined by R.dimen.rounded_corner_radius

Note that this implementation only covers the app open/close and does
NOT include support for special accommodation during app swipe to dismiss (i.e. clipping outline etc).

Bug: 277992557

Test: Tested locally on device
Change-Id: Ib182fa24941b92c3d7cdef6f9337eb175fc2e680
(cherry picked from commit eaa39bd4d77358bd033017797d2376eed5c9dcfe)