Reduce overhead of ApplyState by tracking previous values

Even with pooling applied, there are overheads involved with transforms
when quickly cycling through the carousel.

The main goal here is to reduce the transforms in cases the reuse is
still in the same state. Avoiding firing `FadeIn` and `FadeOut` are the
main areas of saving.

osu.Game/Screens/Select/Carousel/DrawableCarouselBeatmap.cs

@@ -71,6 +71,9 @@ namespace osu.Game.Screens.Select.Carousel
         {
             beatmapInfo = panel.BeatmapInfo;
             Item = panel;
+
+            // Difficulty panels should start hidden for a better initial effect.
+            Hide();
         }
 
         [BackgroundDependencyLoader(true)]