Collapse bubbles when drag and drop is initiated

Dragging a notification into split screen would fail if bubbles
were expanded while performing this action. I think it makes sense
to collapse the stack if its open when drag and drop for an app
starts.

Bug: 223909931
Test: atest DragAndDropControllerTest
Test: manual - have bubbles expanded
             - swipe down the shade, long press on a notification
               and drag it
             => bubbles are collapsed and the notif is able to be
                put into split screen.
Change-Id: Ib5160b3d772452f1cdd704926887bd38a5fd1ef1