appDisplay: Use icon-size instead of width/height for system actions

When creating an icon for the system actions search provider, set the
icon size using StIcons own icon-size property instead of ClutterActors
width and height property. That ensures the scale factor is applied and
the icon will be properly scaled on hiDPI screens.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1686>

js/ui/appDisplay.js

@@ -1432,8 +1432,7 @@ var AppSearchProvider = class AppSearchProvider {
 
                 const createIcon = size => new St.Icon({
                     icon_name: iconName,
-                    width: size,
-                    height: size,
+                    icon_size: size,
                     style_class: 'system-action-icon',
                 });