Introduce TaskOrganizer

A first take at the TaskOrganizer API for allowing SysUI to control task presentation.
In this CL we introduce the first two primitives:
        1. The interface itself for implementation by SysUI
        2. Support for organizing a given windowing mode (but atm really only PIP)
We include a sample app that manages the PIP from an APPLICATION_OVERLAY window.

Bug: 139371701
Test: wmtests/TaskOrganizerTests. TaskOrganizerPipTest
Change-Id: I44a8ed311bc5f06285bba2c6ff3b37a7d19a9190