DCOM-310: Analyze if it is possible to map identifiers as a collection of property mappings

[doctrinebot]

Jira issue originally created by user @Ocramius:

Hibernate 5 maps "identifiers" as a specialized type of property mappings (DCOM-309).

It may be possible to store the identifier mappings as a set of property mappings, then reuse that concept to validate identifiers and also convert them very quickly to DB-level types.