Support for RETURNING clause of JSON_QUERY

<JSON query> ::=
  JSON_QUERY <left paren>
      <JSON API common syntax>
      [ <JSON output clause> ]
      [ <JSON query wrapper behavior> WRAPPER ]
      [ <JSON query quotes behavior> QUOTES [ ON SCALAR STRING ] ]
      [ <JSON query empty behavior> ON EMPTY ]
      [ <JSON query error behavior> ON ERROR ]
      <right paren>

<JSON output clause> ::=
  RETURNING <data type>
      [ FORMAT <JSON representation> ]