workspace: Pass device to startDrag()

This is necessary to make DnD operations work from tablet devices on
wayland, as it's not the same onscreen pointer sprite than mice. Fixes
window DnD in the overview on tablet devices, no longer having them stick
to the wrong pointer.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/897

js/ui/workspace.js

@@ -431,7 +431,7 @@ var WindowClone = GObject.registerClass({
                     return;
                 let [x, y] = action.get_coords();
                 action.release();
-                this._draggable.startDrag(x, y, global.get_current_time(), this._dragTouchSequence);
+                this._draggable.startDrag(x, y, global.get_current_time(), this._dragTouchSequence, event.get_device());
             });
         } else {
             this.emit('show-chrome');