Upgrade to Bean Validation 2.0 and Hibernate Validator 6.0 in ee8.preview.mode

We would like to upgrade Hibernate Validator to 6.0.7.Final in WildFly 12.

Here is our migration guide:
https://developer.jboss.org/wiki/HibernateValidatorMigrationGuide#jive_content_id_60x

You'll notice that in 6.0.6, we have reintroduced a few APIs that we had removed in the previous versions of 6 for this WF upgrade: we had them deprecated in 5.4 then removed in 6 but as WF is still using 5.3, WF users didn't have any notice of that. That's why we decided to reintroduce them before proposing an upgrade in WildFly.

The other APIs removed were marked as experimental and have been superseded by standard features in Bean Validation 2.0 (which is part of Java EE 8).