Refactoring for immutable nodes

Src/AST/Myc.Ast.Binding.pas

@@ -172,9 +172,9 @@ end;
 function TAstBinder.VisitFunctionCall(const Node: IFunctionCallNode): IAstNode;
 begin
     // --- Transformation: Keyword-as-Function ---
-    if (Node.Callee is TKeywordNode) then
+    if Node.Callee.Kind = akKeyword then
     begin
-        var keywordNode := (Node.Callee as TKeywordNode);
+        var keywordNode := Node.Callee.AsKeyword;
         if Length(Node.Arguments) <> 1 then
             raise EArgumentException.CreateFmt(
                 'Keyword :%s expects exactly one argument (the record/map), but got %d',