Initial implemention of the No Release mod

This commit adds a new osu!mania mod No Release that relaxes tail
judgements. The current implementation automatically awards Perfect
(or Meh if the hold note is broken midway) for a hold note tail at
the end of its Perfect window, as long as it is held by then.

Tests are pending for the next commit.

osu.Game.Rulesets.Mania/ManiaRuleset.cs

@@ -241,6 +241,7 @@ public override IEnumerable<Mod> GetModsFor(ModType type)
                         new ManiaModEasy(),
                         new ManiaModNoFail(),
                         new MultiMod(new ManiaModHalfTime(), new ManiaModDaycore()),
+                        new ManiaModNoRelease(),
                     };
 
                 case ModType.DifficultyIncrease:

osu.Game.Rulesets.Mania/Mods/ManiaModNoRelease.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 osu.Framework.Localisation;
+using osu.Game.Rulesets.Mania.Objects.Drawables;
+using osu.Game.Rulesets.Mods;
+using osu.Game.Rulesets.Objects.Drawables;
+using osu.Game.Rulesets.Scoring;
+
+namespace osu.Game.Rulesets.Mania.Mods
+{
+    public class ManiaModNoRelease : Mod, IApplicableToDrawableHitObject
+    {
+        public override string Name => "No Release";
+
+        public override string Acronym => "NR";
+
+        public override LocalisableString Description => "No more timing the end of hold notes.";
+
+        public override double ScoreMultiplier => 0.9;
+
+        public override ModType Type => ModType.DifficultyReduction;
+
+        public void ApplyToDrawableHitObject(DrawableHitObject drawable)
+        {
+            if (drawable is DrawableHoldNote hold)
+            {
+                hold.HitObjectApplied += dho =>
+                {
+                    ((DrawableHoldNote)dho).Tail.LateReleaseResult = HitResult.Perfect;
+                };
+            }
+        }
+    }
+}

osu.Game.Rulesets.Mania/Objects/Drawables/DrawableHoldNoteTail.cs

@@ -3,6 +3,7 @@
 
 #nullable disable
 
+using System.Diagnostics;
 using osu.Framework.Graphics;
 using osu.Framework.Input.Events;
 using osu.Game.Rulesets.Scoring;
@@ -18,6 +19,11 @@ public partial class DrawableHoldNoteTail : DrawableNote
 
         protected internal DrawableHoldNote HoldNote => (DrawableHoldNote)ParentHitObject;
 
+        /// <summary>
+        /// The minimum uncapped result for a late release.
+        /// </summary>
+        public HitResult LateReleaseResult { get; set; } = HitResult.Miss;
+
         public DrawableHoldNoteTail()
             : this(null)
         {
@@ -32,9 +38,23 @@ public DrawableHoldNoteTail(TailNote tailNote)
 
         public void UpdateResult() => base.UpdateResult(true);
 
-        protected override void CheckForResult(bool userTriggered, double timeOffset) =>
+        protected override void CheckForResult(bool userTriggered, double timeOffset)
+        {
+            Debug.Assert(HitObject.HitWindows != null);
+
             // Factor in the release lenience
-            base.CheckForResult(userTriggered, timeOffset / TailNote.RELEASE_WINDOW_LENIENCE);
+            double scaledTimeOffset = timeOffset / TailNote.RELEASE_WINDOW_LENIENCE;
+
+            // Check for late release
+            if (HoldNote.HoldStartTime != null && scaledTimeOffset > HitObject.HitWindows.WindowFor(LateReleaseResult))
+            {
+                ApplyResult(GetCappedResult(LateReleaseResult));
+            }
+            else
+            {
+                base.CheckForResult(userTriggered, scaledTimeOffset);
+            }
+        }
 
         protected override HitResult GetCappedResult(HitResult result)
         {