workspace: Use the new WorkspaceLayout for allocating window clones

workspace: Use the new WorkspaceLayout for allocating window clones

Switch to the new WorkspaceLayout layout manager to allocate the window
clones of the overview properly using Clutters layouting mechanisms.

Since we now no longer make use of the fullGeometry, we can remove the
setFullGeometry() function from the Workspace class. Also we can stop
setting the actualGeometry on the Workspaces and WorkspaceViews and
instead just set the fixed position and size of the views to their
full or actual geometry. This also has the benefit that we no longer
have to set a custom clip, but can simply enable clip_to_allocation.

The geometry needs to be set inside a BEFORE_REDRAW later because
_updateWorkspacesActualGeometry() is called from a notify::allocation
handler.

This isn't doing any animations when showing/hiding the overview yet,
we'll add that in the next commit.

https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1305