[PiP2] Add start delay to app icon overlay fadeout

Same as in PiP1, if entering PiP with app icon overlay,
PiP2 should also use some start delay to fadeout animation.
This allows the app's redraw to not be visible.

The user can still interact with the PiP window throughout the fadeout,
unlike in PiP1 however; so in PiP2, touch interactions are still allowed
early.

Bug: 397984771
Flag: com.android.wm.shell.enable_pip2
Test: swipe PiP to home with invalid src-rect-hint
Change-Id: I8a4a55ab0c5701c31d3e8b5b9540d9b807091e18