HHH-17837 Join + GroupBy: Wrong column used for many-to-many association

[mbladel]

https://hibernate.atlassian.net/browse/HHH-17837

[mbladel]

This PR effectively aligns the behavior of explicit joins with plural paths (i.e. to-many associations) with what was previously done for to-ones: explicitly requesting a join will now always produce an actual join in the generated query, effectively disabling any foreign-key optimizations. This allows us to ensure the correct "side" of the FK is used wrt group by / order by clauses.

Because of the change in behavior, I had to adapt a couple existing tests that were asserting the number of joins in generated queries. See also the Jira comments for more details.

[mbladel]

After initial discussion with @beikov, we opted to preserve foreign-key optimizations whenever possible: we will only force using the association target type's table when the key property being selected is also found in the group by clause of the query. In all other cases, explicit joins will preserve table-group laziness, only initializing it when needed.