[FEATURE] PostgreSQL 18 : add support for RETURNING statement old and new values

[tomershay]

https://www.postgresql.org/docs/18/dml-returning.html

PostgreSQL 18 adds support for OLD and NEW references in a RETURNING statement.
It could be beneficial to add support to this syntax in a more structured way, as by default the old / new prefixes will be just recognized as regular table name prefixes, which shouldn't be the case here.