Indicate whether dropping an app icon was successful or not by using the
newly added `animateLaunchAtPos()` API of AppIcon which starts a zoom
out animation of the icon at the position the drop happened.
To get the position of the drag actor, we have to forward the arguments
passed to `acceptDrop()` and `handleDragOver()` to the internal drag
handlers of the WorkspaceThumbnails. We can use this position directly
without transforming it to stage coordinates because the actor is a
child of `Main.uiGroup` and the animation actor will also be a child of
this container.
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/121
f8e648b7e3