quickSettings: Rename 'label' property to 'title'

We'll soon add a subtitle, so rename the label property to something
that is a bit more semantic.Add a warning when trying to set the old
'label' property.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2619>

js/ui/status/nightLight.js

@@ -17,7 +17,7 @@ const NightLightToggle = GObject.registerClass(
 class NightLightToggle extends QuickToggle {
     _init() {
         super._init({
-            label: _('Night Light'),
+            title: _('Night Light'),
             iconName: 'night-light-symbolic',
             toggleMode: true,
         });