Remove unused internal classes, methods, and comparers (#20746)

- Delete SerialDisposableValue class (zero references across codebase)
- Delete SingleOrDictionary<TKey, TValue> class (zero references across codebase)
- Remove unused CompareRoundingErrors private method from Grid.cs
- Remove unused StarDistributionOrderIndexComparer private class from Grid.cs
- Remove unused DistributionOrderIndexComparer private class from Grid.cs
- Remove unused OnGridVisibilityChanged private method from DatePicker.cs

src/Avalonia.Base/Reactive/SerialDisposableValue.cs

@@ -1,35 +0,0 @@
-using System;
-using System.Threading;
-
-namespace Avalonia.Reactive;
-
-/// <summary>
-/// Represents a disposable resource whose underlying disposable resource can be replaced by another disposable resource, causing automatic disposal of the previous underlying disposable resource.
-/// </summary>
-internal sealed class SerialDisposableValue : IDisposable
-{
-    private IDisposable? _current;
-    private bool _disposed;
-    
-    public IDisposable? Disposable
-    {
-        get => _current;
-        set
-        {
-            _current?.Dispose();
-            _current = value;
-            
-            if (_disposed)
-            {
-                _current?.Dispose();
-                _current = null;
-            }
-        }
-    }
-
-    public void Dispose()
-    {
-        _disposed = true;
-        _current?.Dispose();
-    }
-}

src/Avalonia.Base/Utilities/SingleOrDictionary.cs

@@ -1,144 +0,0 @@
-using System;
-using System.Collections;
-using System.Collections.Generic;
-using System.Diagnostics.CodeAnalysis;
-using System.Linq;
-
-namespace Avalonia.Utilities
-{
-    /// <summary>
-    /// Stores either a single key value pair or constructs a dictionary when more than one value is stored.
-    /// </summary>
-    /// <typeparam name="TKey">The type of the key.</typeparam>
-    /// <typeparam name="TValue">The type of the value.</typeparam>
-    internal class SingleOrDictionary<TKey, TValue> : IEnumerable<KeyValuePair<TKey, TValue>>
-        where TKey : notnull
-    {
-        private KeyValuePair<TKey, TValue>? _singleValue;
-        private Dictionary<TKey, TValue>? dictionary;
-
-        public void Add(TKey key, TValue value)
-        {
-            if (_singleValue != null)
-            {
-                dictionary = new Dictionary<TKey, TValue>();
-                ((ICollection<KeyValuePair<TKey, TValue>>)dictionary).Add(_singleValue.Value);
-                _singleValue = null;
-            }
-
-            if (dictionary != null)
-            {
-                dictionary.Add(key, value);
-            }
-            else
-            {
-                _singleValue = new KeyValuePair<TKey, TValue>(key, value);
-            }
-        }
-
-        public bool TryGetValue(TKey key, [MaybeNullWhen(false)] out TValue value)
-        {
-            if (dictionary == null)
-            {
-                if (!_singleValue.HasValue || !EqualityComparer<TKey>.Default.Equals(_singleValue.Value.Key, key))
-                {
-                    value = default;
-                    return false;
-                }
-                else
-                {
-                    value = _singleValue.Value.Value;
-                    return true;
-                }
-            }
-            else
-            {
-                return dictionary.TryGetValue(key, out value);
-            }
-        }
-
-        public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
-        {
-            if (dictionary == null)
-            {
-                if (_singleValue.HasValue)
-                {
-                    return new SingleEnumerator<KeyValuePair<TKey, TValue>>(_singleValue.Value);
-                }
-            }
-            else
-            {
-                return dictionary.GetEnumerator();
-            }
-            return Enumerable.Empty<KeyValuePair<TKey, TValue>>().GetEnumerator();
-        }
-
-        IEnumerator IEnumerable.GetEnumerator()
-        {
-            return GetEnumerator();
-        }
-
-        public IEnumerable<TValue> Values
-        {
-            get
-            {
-                if(dictionary == null)
-                {
-                    if (_singleValue.HasValue)
-                    {
-                        return new[] { _singleValue.Value.Value };
-                    }
-                }
-                else
-                {
-                    return dictionary.Values;
-                }
-                return Enumerable.Empty<TValue>();
-            }
-        }
-
-        private class SingleEnumerator<T> : IEnumerator<T>
-        {
-            private readonly T value;
-            private int index = -1;
-
-            public SingleEnumerator(T value)
-            {
-                this.value = value;
-            }
-
-            public T Current
-            {
-                get
-                {
-                    if (index == 0)
-                    {
-                        return value;
-                    }
-                    else
-                    {
-                        throw new InvalidOperationException();
-                    }
-                }
-            }
-
-            object? IEnumerator.Current => Current;
-
-            public void Dispose()
-            {
-            }
-
-            public bool MoveNext()
-            {
-                index++;
-                return index < 1;
-            }
-
-            public void Reset()
-            {
-                index = -1;
-            }
-        }
-
-    }
-}

src/Avalonia.Controls/DateTimePickers/DatePicker.cs

@@ -103,8 +103,6 @@ namespace Avalonia.Controls
             SetCurrentValue(MaxYearProperty, new DateTimeOffset(now.Date.Year + 100, 12, 31, 0, 0, 0, now.Offset));
         }
 
-        private static void OnGridVisibilityChanged(DatePicker sender, AvaloniaPropertyChangedEventArgs e) => sender.SetGrid();
-
         public string DayFormat
         {
             get => GetValue(DayFormatProperty);

src/Avalonia.Controls/Grid.cs

@@ -2278,25 +2278,6 @@ namespace Avalonia.Controls
             return null;
         }
 
-        /// <summary>
-        /// Sorts row/column indices by rounding error if layout rounding is applied.
-        /// </summary>
-        /// <param name="x">Index, rounding error pair</param>
-        /// <param name="y">Index, rounding error pair</param>
-        /// <returns>1 if x.Value > y.Value, 0 if equal, -1 otherwise</returns>
-        private static int CompareRoundingErrors(KeyValuePair<int, double> x, KeyValuePair<int, double> y)
-        {
-            if (x.Value < y.Value)
-            {
-                return -1;
-            }
-            else if (x.Value > y.Value)
-            {
-                return 1;
-            }
-            return 0;
-        }
-
         /// <summary>
         /// Calculates final (aka arrange) size for given range.
         /// </summary>
@@ -2985,88 +2966,6 @@ namespace Avalonia.Controls
             }
         }
 
-        /// <summary>
-        /// StarDistributionOrderIndexComparer.
-        /// </summary>
-        private class StarDistributionOrderIndexComparer : IComparer
-        {
-            private readonly IReadOnlyList<DefinitionBase> definitions;
-
-            internal StarDistributionOrderIndexComparer(IReadOnlyList<DefinitionBase> definitions)
-            {
-                this.definitions = definitions ?? throw new ArgumentNullException(nameof(definitions));
-            }
-
-            public int Compare(object? x, object? y)
-            {
-                int? indexX = x as int?;
-                int? indexY = y as int?;
-
-                DefinitionBase? definitionX = null;
-                DefinitionBase? definitionY = null;
-
-                if (indexX != null)
-                {
-                    definitionX = definitions[indexX.Value];
-                }
-                if (indexY != null)
-                {
-                    definitionY = definitions[indexY.Value];
-                }
-
-                int result;
-
-                if (!CompareNullRefs(definitionX, definitionY, out result))
-                {
-                    result = definitionX.SizeCache.CompareTo(definitionY.SizeCache);
-                }
-
-                return result;
-            }
-        }
-
-        /// <summary>
-        /// DistributionOrderComparer.
-        /// </summary>
-        private class DistributionOrderIndexComparer : IComparer
-        {
-            private readonly IReadOnlyList<DefinitionBase> definitions;
-
-            internal DistributionOrderIndexComparer(IReadOnlyList<DefinitionBase> definitions)
-            {
-                this.definitions = definitions ?? throw new ArgumentNullException(nameof(definitions));
-            }
-
-            public int Compare(object? x, object? y)
-            {
-                int? indexX = x as int?;
-                int? indexY = y as int?;
-
-                DefinitionBase? definitionX = null;
-                DefinitionBase? definitionY = null;
-
-                if (indexX != null)
-                {
-                    definitionX = definitions[indexX.Value];
-                }
-                if (indexY != null)
-                {
-                    definitionY = definitions[indexY.Value];
-                }
-
-                int result;
-
-                if (!CompareNullRefs(definitionX, definitionY, out result))
-                {
-                    double xprime = definitionX.SizeCache - definitionX.MinSizeForArrange;
-                    double yprime = definitionY.SizeCache - definitionY.MinSizeForArrange;
-                    result = xprime.CompareTo(yprime);
-                }
-
-                return result;
-            }
-        }
-
         /// <summary>
         /// RoundingErrorIndexComparer.
         /// </summary>