Use simple object field for Node.UserData for now

Author: adams85

src/Acornima/Ast/Node.cs

@@ -43,23 +43,13 @@ protected Node(NodeType type)
     internal SourceLocation _location;
     public SourceLocation Location { [MethodImpl(MethodImplOptions.AggressiveInlining)] get => _location; init => _location = value; }
 
-    private AdditionalDataSlot _additionalDataSlot;
-
-    //// TODO: allow multiple pieces of user data?
-
     /// <summary>
     /// Gets or sets the arbitrary, user-defined data object associated with the current <see cref="Node"/>.
     /// </summary>
     /// <remarks>
     /// The operation is not guaranteed to be thread-safe. In case concurrent access or update is possible, the necessary synchronization is caller's responsibility.
     /// </remarks>
-    public object? UserData
-    {
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        get => _additionalDataSlot.PrimaryData;
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        set => _additionalDataSlot.PrimaryData = value;
-    }
+    public object? UserData { [MethodImpl(MethodImplOptions.AggressiveInlining)] get; [MethodImpl(MethodImplOptions.AggressiveInlining)] set; }
 
     protected internal abstract object? Accept(AstVisitor visitor);