windowManager: Add shortcut for toggling quick settings

Ever since the various status menus were combined into a single
aggregate menu, the menu has been an important entry point. Alas,
we never got around to adding a shortcut for it, not least because
there never was a good candidate.

We just freed super+s which works as either "system" or
"(quick) settings", so use that.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5670

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2716>

js/ui/panel.js

@@ -640,6 +640,10 @@ class Panel extends St.Widget {
         this._toggleMenu(this.statusArea.dateMenu);
     }
 
+    toggleQuickSettings() {
+        this._toggleMenu(this.statusArea.quickSettings);
+    }
+
     closeCalendar() {
         this._closeMenu(this.statusArea.dateMenu);
     }