Add ability to swap docked/fullscreen stack

Adds tap affordance that moves all tasks of the docked
stack into the fullscreen stack as well as moves the top task
of the fullscreen stack into the docked stack.

Also make sure not to trigger focus switch when tapping the divider
handle. For that, add a method so SysUI can specify the touchable
region which then gets excludes for the focus switch touch region.

Bug: 27358134
Change-Id: I34f39c53cacc0b9c00f87a792b88c3f64a5f61e1