Allow org.hibernate.type.Type to contribute AuxiliaryDatabaseObject

[beikov]

It is desirable to support DDL generation and validation for array and struct types when these are introduced.

My suggestion is to add a method to the contracts BasicType and CompositeType:

default void addDatabaseObjects(Database database) {
}

An array type or struct type could then add objects for their type definitions if necessary. I think it might be appropriate to create a dedicated implementation of ContributableDatabaseObject for this purpose that captures the structure. I propose the following contracts (just sketched out, not final):

class UserDefinedType implements ContributableDatabaseObject {
    QualifiedName getName() {..}
    Collection<Column> getColumns() {..}
}

Essentially, this is like a subset of Table composed of just a name and the columns. If nobody objects, I would consider extracting this as super type. Namespace will then manage a map for user defined types. DatabaseInformation would receive a new method for accessing the user type information from the database.

Conclusion: In the end, we didn't need this on Type to implement DDL support.