dnd: Don't use transformed size to calculate parent scale when restoring

Some drag actor parents might change their width to 0 after the drag
actor has been removed. If the drag is now canceled and the drag actor
is animated to return to the current parent position and scale, this
scale can not be determined and falls back to 1.0. This might be wrong
and can result in the drag actor being too large/small at the end of the
return animation.

To avoid this calculate the scale of the parent by recursively
calculating the product of its parents individual scales.

Fixes https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/4017