fix: declare getMetaDataSymbol() as returning symbol | string

src/fxp.d.ts

@@ -724,7 +724,7 @@ export class XMLParser {
    * The XMLMetaData property is only present when {@link X2jOptions.captureMetaData}
    * is true in the options.
    */
-  static getMetaDataSymbol(): Symbol;
+  static getMetaDataSymbol(): symbol | string;
 }
 
 /**