Hibernate-reactive: replicate HHH-14312

Uffff. This looks like it is going to be painful to untangle. The whole type hierarchy of batching loaders has completely changed, and it looks like our batch loading support is going to need to be reimplemented from scratch.

@DavideD @Sanne in terms of the roadmap ya'll are working out, this is perhaps the highest-priority major issue after the schema export stuff.

@gbadner has offered to work on this one, which is awesome because she knows this part of the codebase much better than we do.

@gavinking, is the objective of this issue just to reproduce with a test?

Also, how does this compare in priority to finishing support for SchemaMigrator/SchemaValidator for the remaining dialects (SQL Server and DB2)?

@gbadner it's about reworking the code we have for batch loading to adapt it to the newly-refactored code in ORM.

But the schema export stuff is definitely a higher priority.

Oh, ok, got it. I wasn't sure if "replicate" meant "reproduce".