Launch overview instance of app for taskbar in Overview

* This only works for fullscreen tasks, app pairs aren't
properly launching yet
* We re-layer the leash to be above launcher since live tiles
are originally below
* The new task comes in from TaskAnimationManager#onTaskAppeared

Bug: 316485863
Test: Tested w/ tapping fullscreen apps in overview when
their thumbnail is scrolled off screen. Animation occurs for
both live tile and thumbnail

Change-Id: I5a3c079244a1517becb845ce25ff9f4e671383b1