[Pip-CD] (1/n) Add prototype to move PiP window to another display.

This uses the cursor's position on which display ID it's releasing the
PiP window on and starts a transition to reparent the wct to that
display ID.

Also ensure the PiP bounds are scaled correctly according to the origin
and target display density.

Demo: https://drive.google.com/file/d/1WC6z5ePpG9IeXu-An4oLq-CnsklBVaVS/view
Flag: com.android.window.flags.enable_dragging_pip_across_displays
Test: manual testing & atest
Bug: 383403514
Change-Id: Ief6b15942f9533350e277b0d7d1feb618d4b51da