Reintroduce PARTIAL, but only for non-object hydration.

[beberlei]

As discussed in #8471 (comment), PARTIAL is re-introduced in 3.2 but only when used with non object hydrators, usefully with array hydration.

This will allow retrieval of partial fields with complex entity dql relationships, example:

    $query = $em->createQuery('SELECT partial u.{id, username}, partial a.{id, name} FROM CmsUser u JOIN u.articles a');
    $users = $query->getArrayResult(); // array of partially loaded CmsUser and CmsArticle fields

Todo:

• Test for the partial hydration exception with object hydration mode
• Test for UnitOfWork::createEntity with partial keyword usage.
• Actual test for array hydrator partial usage

Related:

• Undeprecate PARTIAL for array hydration. #11366
• Deprecate Partial Objects #8471