Refactor serialization copying to use source generators (#4286)

Robust.Serialization.Generator/DataDefinitionComparer.cs

@@ -0,0 +1,17 @@
+using System.Collections.Generic;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+
+namespace Robust.Serialization.Generator;
+
+public sealed class DataDefinitionComparer : IEqualityComparer<TypeDeclarationSyntax>
+{
+    public bool Equals(TypeDeclarationSyntax x, TypeDeclarationSyntax y)
+    {
+        return x.Equals(y);
+    }
+
+    public int GetHashCode(TypeDeclarationSyntax type)
+    {
+        return type.GetHashCode();
+    }
+}