Expand PiP with pseudo source rect hint

Expand PiP with pseudo source rect hint if the app does not provide, to
have a unified expand animation experience.

Flag: com.android.wm.shell.enable_pip2
Bug: 416337465
Video: http://recall/-/aaaaaabFQoRHlzixHdtY/5XTkUXJkkL0ND2xHCWIET
Test: atest --iteration 10 WMShellUnitTests:PipExpandAnimatorTest
Test: Manual expand PiP to full-screen, see Video
Change-Id: I9ddbb960981ee5d2b2309a3dff49d34ce4907498