This is should all be done via SQL AST and DomainResult/Initializer/DomainResultAssembler now.

See about having `org.hibernate.metamodel.mapping` extend `org.hibernate.persister.walking` in a deprecated "shadow package" kind of way. Prefer to get rid of `org.hibernate.persister.walking` if that ends up being difficult or not possible - having the separate classes (describing the same general stuff) is not ideal for memory use.