Support joining against a derived table (subquery used as a join target) in HQL.

Hibernate 7 HQL supports the syntax: JOIN (SELECT o.id FROM Order o) ord ON c.id = ord.id

This is parsed via the JoinSubqueryContext grammar rule and produces a QueryPartTableReference in the SQL AST. Currently throws FeatureNotSupportedException with a reference to this ticket. Implementing this would require the $lookup pipeline form (with a nested pipeline and $expr) rather than the simple localField/foreignField form.

Addressing the source code notes tagged with TODO-HIBERNATE-167 is in scope of this ticket.