HHH-13058 Fix issue left join root cannot be replaced by correlated parent in subquery

[NathanQingyangXu]

https://hibernate.atlassian.net/browse/HHH-13058

The current correlated subquery ignores the first left join and ends up with 'inner join' instead invariably. So suppose for the below entities:

@Entity(name = "Task")
public class Task {
    @Id
    Long id;

    @ManyToOne
    Patient patient;
}

@Entity(name = "Patient")
public class Patient {
    @Id
    Long id;

    @ManyToOne
    Site site;
}

@Entity(name = "Site")
public class Site {
    @Id
    Long id;
}

Note that @ManyToOne's optional is true by default.

the following Criteria would skip the Task without Patient:

final Subquery<Task> subquery = outerQuery.subquery( Task.class );
final Root<Task> subtask = subquery.correlate( outerTask );
final From<Task, Patient> patient = subtask.join( Task_.patient, JoinType.LEFT );
final From<Patient, Site> site = patient.join( Patient_.site, JoinType.LEFT );
outerQuery.where(
    builder.exists(
        subquery.select( subtask )
            .where(
                builder.or(
                    patient.isNull(),
                    site.in( validSites )
                )
        )
    )
);

because internally the jpasql generated is:

select generatedAlias0 from Task as generatedAlias0 
where exists (
    select generatedAlias0 
    from generatedAlias0.patient as generatedAlias1 
        left join generatedAlias1.site as generatedAlias2 
    where ( generatedAlias1 is null ) or ( generatedAlias2 in (:param0, :param1) 
))

Note that generatedAlias1 is null can never be true for the left join from Task to Patient has been skipped by correlate parent's alias substitution; but given that Task's Patient is optional we should reserve the left join from Task to Patient.
The fix in this PR is to create the following jpasql instead:

select generatedAlias0 from Task as generatedAlias0 
where exists (
    select generatedAlias0 
    from Task as generatedAlias1 
        left join generatedAlias1.patient as generatedAlias1 
        left join generatedAlias1.site as generatedAlias2 
    where 
        generatedAlias1 = generatedAlias0 and (( generatedAlias1 is null ) or ( generatedAlias2 in (:param0, :param1))
))

The basic idea is to generate new alias for correlated root and add newAlias = oldAlias to the WHERE jpasql clause, thus reserving the LEFT JOIN semantic of the correlated root in subquery.
However, the old pattern still remains for performance reason and the above changes only apply when LEFT JOIN is involved.

[NathanQingyangXu]

Note for v6 porting. The code changes might not be applicable to v6 and nontrivial v6 specific tweaking might be needed, but the testing case is invaluable.

[beikov]

Requires some further work as the implementation produces SQL queries that aren't as efficient as before.

[beikov]

Looking good!