dbusServices/screensaver: Split out public ScreenSaver service

Commit 799bbdb50 split out the public Fdo notification service, so
that any app with permission to talk to org.freedesktop.Notifications
will in fact be limited to that service.

To a somewhat lesser extent this applies to the org.gnome.ScreenSaver
service as well, which some applications still use instead of the
Inhibit portal.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/3452

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1520>

js/ui/shellDBus.js

@@ -367,7 +367,8 @@ var ScreenSaverDBus = class {
         this._dbusImpl = Gio.DBusExportedObject.wrapJSObject(ScreenSaverIface, this);
         this._dbusImpl.export(Gio.DBus.session, '/org/gnome/ScreenSaver');
 
-        Gio.DBus.session.own_name('org.gnome.ScreenSaver', Gio.BusNameOwnerFlags.REPLACE, null, null);
+        Gio.DBus.session.own_name('org.gnome.Shell.ScreenShield',
+            Gio.BusNameOwnerFlags.NONE, null, null);
     }
 
     LockAsync(parameters, invocation) {