Since the regular session also switched to horizontal workspaces,
using a vertical menu has been a bit awkward.
Now that our previews have become more flexible, we can use them
in the collapsed state as well as when embedded into the top bar.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/316>
We currently avoid previews from overflowing in most setups by
artificially limiting them to a maximum of six workspaces.
Add some proper handling to also cover cases where space is more
limited, and to allow removing the restriction in the future.
For that, wrap the previews in an auto-scrolling scroll view
and add overflow indicators on each side.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/316>