Encapsulate mod hotkey selection logic in strategy pattern

osu.Game/Overlays/Mods/Input/ModHotkeyHandler.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.Game.Rulesets.Mods;
+
+namespace osu.Game.Overlays.Mods.Input
+{
+    /// <summary>
+    /// Static factory class for <see cref="IModHotkeyHandler"/>s.
+    /// </summary>
+    public static class ModHotkeyHandler
+    {
+        /// <summary>
+        /// Creates an appropriate <see cref="IModHotkeyHandler"/> for the given <paramref name="modType"/>.
+        /// </summary>
+        public static IModHotkeyHandler Create(ModType modType)
+        {
+            switch (modType)
+            {
+                case ModType.DifficultyReduction:
+                case ModType.DifficultyIncrease:
+                case ModType.Automation:
+                    return SequentialModHotkeyHandler.Create(modType);
+
+                default:
+                    return new NoopModHotkeyHandler();
+            }
+        }
+    }
+}