Serialize Document, a Prolog term representing a GraphQL document
as obtained from graphql_read_document/3 or the graphql/4
quasi-quotation, and unify Codes with the resulting list of
character codes.
Options are a list whose elements are one of:
- separator(+Sep)
- Sep is a list of codes to be used for separating adjancent
GraphQL values in Codes. Defaults to a single space.
This option can be used to separate values with commas
(which are optional throughout GraphQL) by passing
e.g.
separator(`, `).
