Previously, when snapping back a drag actor, we moved it back to its
original stage-relative position and scale. This worked fine if its
parent was still in the same place it was when the drag started, but
failed in cases like the linear workspace layout window drag-and-drop,
where dragging a window would "zoom out" its parent workspace, causing
the snapback to send it to the wrong place.
Fix this by instead snapping the actor back to "where the actor would
have been right now if it were still at its original scale and
position within its original parent actor" rather than "where it was
before the drag started"
https://bugzilla.gnome.org/show_bug.cgi?id=635272
b956c6f093