Return body as string instead of URLSearchParams

Returning the raw URLSearchParams object causes some issues in different environments than node/browser

Author: ale18V

packages/client-core/src/bodySerializer.ts

@@ -79,6 +79,6 @@ export const urlSearchParamsBodySerializer = {
       }
     });
 
-    return data;
+    return data.toString();
   },
 };