Update existing code to use provided substitutes

Author: Patonymous

src/Tools/LeanCode.CodeAnalysis/CodeActions/FixCQRSHandlerNamespaceCodeAction.cs

@@ -115,7 +115,7 @@ CancellationToken cancellationToken
                     }
 
                     var updatedText = (await document.GetTextAsync(cancellationToken)).ToString();
-                    await File.WriteAllTextAsync(newPath, updatedText, cancellationToken);
+                    await MissingFileMethods.WriteAllTextAsync(newPath, updatedText, cancellationToken);
                     File.Delete(document.FilePath);
                 }
             }