Refactor PiP2 resize transitions

Refactor PiP2 resize transitions, e.g.
double-tap, flings, and pinch-to-resize to
use config-at-end flipv2.

This should also allow for faster touch interaction
re-enabling than before with double-taps and pinches,
since the flipv2 moves task maniipulation ownership to Shell.

Also cleaned up PipTransition and PipScheduler to simplify resize logic.

Bug: 376104088
Flag: com.android.wm.shell.enable_pip2
Test: enter PiP and resize PiP by double-tap/pinch
Change-Id: I1f43f639193ab2ac189f23957cf5b82f598afb5f