Implement "classic" mod for all other legacy rulesets

Currently empty, automatically handled in game to not be selectable (see `Mod.HasImplementation`)

osu.Game.Rulesets.Catch/CatchRuleset.cs

@@ -114,6 +114,7 @@ namespace osu.Game.Rulesets.Catch
                     return new Mod[]
                     {
                         new CatchModDifficultyAdjust(),
+                        new CatchModClassic(),
                     };
 
                 case ModType.Automation:

osu.Game.Rulesets.Catch/Mods/CatchModClassic.cs

@@ -0,0 +1,11 @@
+// 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.Rulesets.Catch.Mods
+{
+    public class CatchModClassic : ModClassic
+    {
+    }
+}

osu.Game.Rulesets.Mania/ManiaRuleset.cs

@@ -239,6 +239,7 @@ namespace osu.Game.Rulesets.Mania
                         new ManiaModDualStages(),
                         new ManiaModMirror(),
                         new ManiaModDifficultyAdjust(),
+                        new ManiaModClassic(),
                         new ManiaModInvert(),
                         new ManiaModConstantSpeed()
                     };

osu.Game.Rulesets.Mania/Mods/ManiaModClassic.cs

@@ -0,0 +1,11 @@
+// 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.Rulesets.Mania.Mods
+{
+    public class ManiaModClassic : ModClassic
+    {
+    }
+}

osu.Game.Rulesets.Taiko/Mods/TaikoModClassic.cs

@@ -0,0 +1,11 @@
+// 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.Rulesets.Taiko.Mods
+{
+    public class TaikoModClassic : ModClassic
+    {
+    }
+}

osu.Game.Rulesets.Taiko/TaikoRuleset.cs

@@ -135,6 +135,7 @@ namespace osu.Game.Rulesets.Taiko
                     {
                         new TaikoModRandom(),
                         new TaikoModDifficultyAdjust(),
+                        new TaikoModClassic(),
                     };
 
                 case ModType.Automation: