Use ReferenceEqualityComparer instead of TypeEqualityComparer

Author: MrJul

src/Avalonia.Base/AvaloniaProperty.cs

@@ -32,8 +32,8 @@ public abstract class AvaloniaProperty : IEquatable<AvaloniaProperty>, IProperty
         private Type? _singleHostType;
         private AvaloniaPropertyMetadata? _singleMetadata;
 
-        private readonly Dictionary<Type, AvaloniaPropertyMetadata> _metadata = new(TypeEqualityComparer.Instance);
-        private readonly Dictionary<Type, AvaloniaPropertyMetadata> _metadataCache = new(TypeEqualityComparer.Instance);
+        private readonly Dictionary<Type, AvaloniaPropertyMetadata> _metadata = new(ReferenceEqualityComparer.Instance);
+        private readonly Dictionary<Type, AvaloniaPropertyMetadata> _metadataCache = new(ReferenceEqualityComparer.Instance);
 
         /// <summary>
         /// Initializes a new instance of the <see cref="AvaloniaProperty"/> class.

src/Avalonia.Base/Compatibility/ReferenceEqualityComparer.cs

@@ -0,0 +1,22 @@
+#if NETSTANDARD2_0
+
+using System.Runtime.CompilerServices;
+
+namespace System.Collections.Generic;
+
+internal sealed class ReferenceEqualityComparer : IEqualityComparer<object?>, IEqualityComparer
+{
+    public static ReferenceEqualityComparer Instance { get; } = new();
+
+    private ReferenceEqualityComparer()
+    {
+    }
+
+    public new bool Equals(object? x, object? y)
+        => ReferenceEquals(x, y);
+
+    public int GetHashCode(object? obj)
+        => RuntimeHelpers.GetHashCode(obj);
+}
+
+#endif