Allow exclusion areas in PiP2

Set up Pip interface in PipController in pip2,
so that other components in the host process can
communicate with PiP.

In this specific CL, allow to add exclusion area update
callbacks, that are executed every time PiP bounds change.

This helps avoid back gesture to appear when PiP is stashed for instance
inside the PiP region.

Bug: 352552598
Flag: com.android.wm.shell.enable_pip2_implementation
Test: stash PiP and attempt a back gesture in PiP region
Change-Id: Ic68cf0e960cde77b9dbf88afb09f178edef68b3c