Support the SQL standard JSON_QUERY

[lukaseder]

We already support JSON_VALUE, which can be used to extract a string value from a JSON document. With JSON_QUERY, it's possibly to extract a JSON subdocument.

There are multiple internal usages of N_JSON_QUERY already, so there's room for refactoring. See e.g. https://github.com/jOOQ/jOOQ/issues/10018, where Db2 now usese JSON_QUERY as well.