Introduce `Query::getResultCount`

[quaff]

Hibernate introduce SelectionQuery.getResultCount() since 6.5.0, It's useful for paged query, Query object can be reused for both data and count query.

Query query = entityManager.createQuery(queryString);
query.setFirstResult(10);
query.setMaxResults(10);
result.setTotal(query.getResultCount()); // must ignore `firstResult` and `maxResults`
result.setData(query.getResultList());