PiP: Move menu to SystemWindow.

This is the first step to move the menu to fullscreen, but not quite
yet.

This CL does:
- Move PipMenuView to be attached to SystemWindow, instead of child of
PiP leash
- Use SyncRtSurfaceTransactionApplier to ensure the menu moves along the
PIP leash at the same time when the menu is visible
- Remove setup/destroy code in PipTaskOrganizer with SurfaceViewHost
- Expose Window information to Accessibility services
- Refactor ShellRoot to take in a Layer type instead of windowType
instead

Bug: 161710689
Bug: 170151121
Bug: 169894316
Bug: 152738416
Test: Manual

Change-Id: I73c26f96784b35b9bb9a4bea452df55cf5913278