cleanup: Prefer using Color struct constructor

Instead of Color.from_pixel or Color.new as both would be removed
to simplify the Color API

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3367>

js/ui/windowManager.js

@@ -149,7 +149,12 @@ class WindowDimmer extends Clutter.BrightnessContrastEffect {
 
     setDimmed(dimmed, animate) {
         let val = 127 * (1 + (dimmed ? 1 : 0) * DIM_BRIGHTNESS);
-        let color = Clutter.Color.new(val, val, val, 255);
+        const color = new Clutter.Color({
+            red: val,
+            green: val,
+            blue: val,
+            alpha: 255,
+        });
 
         this.actor.ease_property(`@effects.${this.name}.brightness`, color, {
             mode: Clutter.AnimationMode.LINEAR,