Quote a PostgreSQL identifier, escaping embedded double-quotes.
Use this instead of duplicating format!("\"{}\"", s.replace('"', "\"\"")) in every module.
Validate a privilege specification for GRANT/REVOKE. Accepts a
comma-separated list of known privilege keywords (case-insensitive), e.g.
"SELECT, INSERT" or "ALL PRIVILEGES". Rejects anything else so the
value can be safely interpolated into the statement.