workspace: Position clones using width and height instead of scale

workspace: Position clones using width and height instead of scale

Since we now have a layout manager for the WindowClone that allows
allocating it a size that isn't the absolute size of the window, we can
now give the WindowClone an artificial size and it will get scaled
accordingly.

So make use of that and stop positioning WindowClones using fixed
position and scale and use a fixed position and fixed size instead. This
will make it easier to use a ClutterLayoutManager to allocate the
WindowClones, because layout managers should only set the allocation of
their children, not the scale.

https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1294