WIP: Touch window dragging fixes
Window dragging on touchscreen devices will cause window jumps in certain situations, also using the Super+drag shortcut still showed the overview afterwards. Fix that and also lay the foundation in case we decide to allow window interaction during window grabs using the touchscreen.
Marked as WIP because
shell_global_sync_pointer causes some windows to warp underneath the mouse pointer after the grab op is started. So this needs to wait until we got rid of sync_pointer.
Depends on gnome-shell!519