Make beatmap detail area abstractable

osu.Game/Screens/Select/BeatmapDetailAreaTabItem.cs

@@ -0,0 +1,35 @@
+// 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.Screens.Select
+{
+    public abstract class BeatmapDetailAreaTabItem : IEquatable<BeatmapDetailAreaTabItem>
+    {
+        /// <summary>
+        /// The name of this tab, to be displayed in the tab control.
+        /// </summary>
+        public abstract string Name { get; }
+
+        /// <summary>
+        /// Whether the contents of this tab can be filtered by the user's currently-selected mods.
+        /// </summary>
+        public virtual bool FilterableByMods => false;
+
+        public override string ToString() => Name;
+
+        public bool Equals(BeatmapDetailAreaTabItem other)
+        {
+            if (ReferenceEquals(null, other)) return false;
+            if (ReferenceEquals(this, other)) return true;
+
+            return Name == other.Name;
+        }
+
+        public override int GetHashCode()
+        {
+            return Name != null ? Name.GetHashCode() : 0;
+        }
+    }
+}