Add support for multiple generic embeddable properties in MappedSuperclass

At the moment an @Entity can extend a @MappedSuperclass which has two or more generic embeddable properties. This will work, but when trying to query the actual properties inside the concrete embeddable types (as opposed to the generic ones) an error will be thrown because we have no way of retrieving them.

fixes embeddable-typed declaredProperties registration for generic embeddables on the superclass, and has prepared a foundation to register the actual concrete embeddable types that for now is only used for identifiers:

• org.hibernate.metamodel.model.domain.AbstractManagedType.InFlightAccessImpl#addConcreteEmbeddableAttribute

• org.hibernate.metamodel.model.domain.AbstractManagedType#findConcreteEmbeddableAttribute

This issue should address resolving concrete embeddable types for non-identifier properties.