Move classes to local namespaces

Also renames test scene to more appropriate name.

osu.Game/Screens/Play/DimmableStoryboard.cs

@@ -0,0 +1,55 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Allocation;
+using osu.Game.Graphics.Containers;
+using osu.Game.Storyboards;
+using osu.Game.Storyboards.Drawables;
+
+namespace osu.Game.Screens.Play
+{
+    /// <summary>
+    /// A container that handles <see cref="Storyboard"/> loading, as well as applies user-specified visual settings to it.
+    /// </summary>
+    public class DimmableStoryboard : UserDimContainer
+    {
+        private readonly Storyboard storyboard;
+        private DrawableStoryboard drawableStoryboard;
+
+        public DimmableStoryboard(Storyboard storyboard)
+        {
+            this.storyboard = storyboard;
+        }
+
+        [BackgroundDependencyLoader]
+        private void load()
+        {
+            initializeStoryboard(false);
+        }
+
+        protected override void LoadComplete()
+        {
+            ShowStoryboard.BindValueChanged(_ => initializeStoryboard(true), true);
+            base.LoadComplete();
+        }
+
+        protected override bool ShowDimContent => ShowStoryboard.Value && UserDimLevel.Value < 1;
+
+        private void initializeStoryboard(bool async)
+        {
+            if (drawableStoryboard != null)
+                return;
+
+            if (!ShowStoryboard.Value)
+                return;
+
+            drawableStoryboard = storyboard.CreateDrawable();
+            drawableStoryboard.Masking = true;
+
+            if (async)
+                LoadComponentAsync(drawableStoryboard, Add);
+            else
+                Add(drawableStoryboard);
+        }
+    }
+}