Add basic mania skin parsing

osu.Game/Skinning/LegacyManiaSkinConfiguration.cs

@@ -0,0 +1,30 @@
+// 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 System;
+
+namespace osu.Game.Skinning
+{
+    public class LegacyManiaSkinConfiguration
+    {
+        public readonly int Keys;
+
+        public readonly float[] ColumnLineWidth;
+        public readonly float[] ColumnSpacing;
+        public readonly float[] ColumnWidth;
+
+        public float HitPosition = 124.8f; // (480 - 402) * 1.6f
+
+        public LegacyManiaSkinConfiguration(int keys)
+        {
+            Keys = keys;
+
+            ColumnLineWidth = new float[keys + 1];
+            ColumnSpacing = new float[keys - 1];
+            ColumnWidth = new float[keys];
+
+            ColumnLineWidth.AsSpan().Fill(2);
+            ColumnWidth.AsSpan().Fill(48);
+        }
+    }
+}