Currently does nothing. When we're in screencast mode, we hide the
screenshot preview because screencast doesn't start until the capture
button is pressed.
The window selection is currently left as is, but it should probably be
changed to something closer to a real overview, showing windows in
real-time.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2103>
497d9f32eb