1e2a10f83b
When passing an invalid or unknown app ID to FocusApp(), we currently open the app picker and silently fail to select the desired app. Instead of half-working like that, make it clear that the argument was invalid by returning an appropriate error. (It's easy to get the ID wrong, as unlike appstream/flatpak IDs, we include the ".desktop" suffix). Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/337>