Do not expand PiP upon lock screen open

This is a counterpart of what's in PiP1:

When tapping on the lock screen notification posted by an Activity in
PiP mode, do not try to expand it to full-screen mode.

Flag: com.android.wm.shell.enable_pip2
Bug: 399521216
video: http://recall/-/aaaaaabFQoRHlzixHdtY/cZqtGRRLtuv5UliDil1VJZ
Test: Follow the reproduce steps in bug, see also the Video
Change-Id: Id90701f31ba488ea7ced5f8e002222ab7019ca14