quickSettings: Hide separator when menu button is hidden

Since commit eeddf49371, the menu button in toggles is separated
by an actual widget rather than just CSS borders.

However the menu button can be hidden, in which case the menu toggle
acts as a regular quick toggle. The separator shouldn't be visible
either in that case, so hide it.

Closes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/8159
Fixes: eeddf49371 ("style: Improve the styles for the separation in quick setting buttons")
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3621>

js/ui/quickSettings.js

@@ -189,6 +189,10 @@ export const QuickMenuToggle = GObject.registerClass({
         });
         this._box.add_child(this._menuButton);
 
+        this._menuButton.bind_property('visible',
+            separator, 'visible',
+            GObject.BindingFlags.SYNC_CREATE);
+
         this.bind_property('toggle-mode',
             contents, 'toggle-mode',
             GObject.BindingFlags.SYNC_CREATE);