Previously, in the in-memory sorting module
`LocalAggregationSorterListener` only the aggregate functions where used
(grabbed by the `sortingColumns`). As a consequence, if the ORDER BY
was also using columns of the GROUP BY clause, (especially in the case
of higher priority - before the aggregate functions) wrong results were
produced. E.g.:
```
SELECT gender, MAX(salary) AS max FROM test_emp
GROUP BY gender
ORDER BY gender, max
```

Add all columns of the ORDER BY to the `sortingColumns` so that the
`LocalAggregationSorterListener` can use the correct comparators in
the underlying PriorityQueue used to implement the in-memory sorting.

Fixes: elastic#50355