Prevent dropping a drag from TaskbarAllApps in Overview

* Don't close TaskbarAllApps once drag starts
(see comment in code regarding needing multiple shared drag
layers)
* Hide app menu split options for taskbar in overview
* One TODO is that the animation needs to be tweaked
because the scale of the icon when it's returned is too large.
* I think maybe we have to change the
TaskbarDragController#mDragIconSize since that gets directly
set from a resource. Unclear.

Test: Dragged in TaskbarAllApps in overivew and in split
select, app returned to original position and not taskbar
Bug: 251747761

Change-Id: I785f34b0bdb0b0abfc440450494074f8dfe7c31a