Implement manually entering PiP flow

It is possible for the client to request
enter PiP directly outside of lifecycle callbacks
(such as onUserLeaveHint). When this direct request comes in
we should run BOUNDS animation instead of ALPHA irrespective of
auto-enter flag value.

We are resolving the type of the animation on the Shell side
by looking at the TransitionInfo before playing the animation.

Bug: 317269218
Test: request enterPictureInPictureMode() directly from client
Change-Id: Ibc3645b5a1ed949bcfaa716f8555cc5179e6b291