TypedQuery inspection through its String representations seems to be a bit flaky in Hibernate 6 still [0]. Tweaked the code to extract a query string from a query object to try the new way first but fall back to the old way, as this seems to work under some conditions, too. Adapted the test case in which we could rather inspect the new SqmQuery API for test result verification.
Re-bootstrapping the EntityManagerFactory for the same persistence unit causes the second bootstrap to fail als apparently foreign key names are randomized and the second bootstrap doesn't create a new constraint but tries to work with a new name. Tweaked the offending test case to reuse the existing EMF declaration as it actually only tests the qualified wiring into clients.
Applying an entity graph is causing a StackOverflow in current Hibernate 6. Filed an issue [1] and disabled the test case for now.
Dial back on the flip to use String as parameter type for like expression escape characters as Eclipselink rejects that. The JPA spec chapter 4.2.10 allows both Character and String to be used. Filed [2] with Hibernate to ask for reintroduction of the support for characters and commented out the test cases for now.
Deprecated CustomHsqlHibernateJpaVendorAdapter as it's not needed on Hibernate 6 anymore. Rewrote HibernateJpaParametersParameterAccessor to use Hibernate 6 API.
Add Hibernate 6 upgrade information to the reference docs.
Related ticket: #2423.
[0] https://hibernate.atlassian.net/browse/HHH-15389
[1] https://hibernate.atlassian.net/browse/HHH-15391
[2] https://hibernate.atlassian.net/browse/HHH-15392
Spring Data JPA is now a multimodule project.
The artifacts build are still separate, except for the documentation which is now a single one.
Closes # 2316
