Use XSD groups for common stuff in schemas

To help with any on-going maintenance of schema(s), it may be better to use XSD groups to extract common stuff. E.g. move things that are common across ``, ``, ``, ... into a group.

see also https://github.com/jakartaee/persistence/pull/541#issuecomment-1783763285

No schema file or test is named. Locate the XSD definitions for , , and , compare their shared declarations, and determine which can be extracted into XSD groups; done means the schemas retain their behavior while common structure is centralized.

Written by the indexing model from the issue text.