Add skin components and interfaces

osu.Game/Screens/Play/HUD/IComboCounter.cs

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+// 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.Bindables;
+using osu.Framework.Graphics;
+
+namespace osu.Game.Screens.Play.HUD
+{
+    /// <summary>
+    /// An interface providing a set of methods to update a combo counter.
+    /// </summary>
+    public interface IComboCounter : IDrawable
+    {
+        /// <summary>
+        /// The current combo to be displayed.
+        /// </summary>
+        Bindable<int> Current { get; }
+    }
+}

osu.Game/Skinning/HUDSkinComponent.cs

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+// 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.Linq;
+
+namespace osu.Game.Skinning
+{
+    public class HUDSkinComponent : ISkinComponent
+    {
+        public readonly HUDSkinComponents Component;
+
+        public HUDSkinComponent(HUDSkinComponents component)
+        {
+            Component = component;
+        }
+
+        protected virtual string ComponentName => Component.ToString();
+
+        public string LookupName =>
+            string.Join("/", new[] { "HUD", ComponentName }.Where(s => !string.IsNullOrEmpty(s)));
+    }
+}

osu.Game/Skinning/HUDSkinComponents.cs

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+// 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.
+
+namespace osu.Game.Skinning
+{
+    public enum HUDSkinComponents
+    {
+        ComboCounter
+    }
+}