Add parameter variations to JSON.stringify

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify?redirectlocale=en-US&redirectslug=JavaScript%2FReference%2FGlobal_Objects%2FJSON%2Fstringify

JSON.stringify can accept null as a replacer parameter and string as a spacer. This patch adds support of them.