Refactor 3-btn-nav with flipv2

Refactor the 3-button-nav enter PiP
bounds animation and transition flow
incorporating the new config-at-end flipv2 approach.

This should reduce the delay to reenable PiP interactions
after enterin PiP, as well as remove need for
setBoundsChangeTransactions.

Also separate enter from expand animator since the animation
logic for these two is going to be inherently different -
as one uses config-at-end flipv2 and the other uses a generic
transition.

Bug: 350801661
Flag: com.android.wm.shell.enable_pip2
Test: atest AutoEnterPipWithSourceRectHintTest
Change-Id: I8a963487db49148db83c6065a983668bf6d3374d