[PIP2] Add bounds animator for enter/exit pip

Adds bounds animator for entering and exiting pip. This currently
implements the basic portrait case, and a follow up CL will add
rotation.

Test: manual check
Flag: com.android.wm.shell.enable_pip2_implementation
Bug: b/350801661
Change-Id: Ib570f7fa4f29cf6aa303e5c23fed7de7ffc63b6d
2 files changed