Use org.freedesktop.ScreenSaver interface instead of gnome's one

[pa-sowa]

Now it should work on most Linux desktop environments and not only on Gnome. Tested on KDE.

[W-Floyd]

This doesn't seem to be implemented under GNOME (ugh). Perhaps we should detect if we're running under GNOME, and use the old method if so, but otherwise use the proposed call? XDG_CURRENT_DESKTOP should be the required variable - I can work on this, or let you add that if you want.

Edit: Quickly tested this

    case "${XDG_CURRENT_DESKTOP}" in
    "GNOME")
        dbus-send --print-reply --session --type=method_call --dest=org.gnome.ScreenSaver /org/gnome/ScreenSaver org.gnome.ScreenSaver.GetActive | tail -n 1 | grep -Eo '[^ ]*$'
        ;;
    *)
        dbus-send --print-reply --session --type=method_call --dest=org.freedesktop.ScreenSaver /ScreenSaver org.freedesktop.ScreenSaver.GetActive | tail -n 1 | grep -Eo '[^ ]*$'
        ;;

    esac

If that works for you, you can commit it and I'll merge. Thanks for taking the time to look at this!

[pa-sowa]

After some research, I found out that this isn't part of the official freedesktop specification. It was introduced by KDE but unfortunately Gnome didn't follow (https://gitlab.gnome.org/GNOME/gnome-settings-daemon/-/issues/632).
For that reason, I think it's better to make it explicit in code which DEs are supported.

[W-Floyd]

Good catch. I'm fine with DE specific code, but I do want a fallthrough for all other DEs, even if it's just an error stating "unknown DE, sorry". I'll go ahead and merge for now though, thanks!