'Drag and drop failed' animation

If the drop has not been consumed (DragState.mDragResult is false)
the drag shadow surface is not immediately destroyed, but animated
back into the position where the drag started.

The current animation is an OK placeholder, still waiting for the
final word from UX.

Bug: 24415573

Change-Id: Ia30135ce1e85655c8ba16e28dc69f0ebf9b36239