opt: null_ordered_last with DISTINCT unexpectedly errors

Setting `null_order_last=true` can cause queries with `DISTINCT` expressions to incorrectly error. See the reproduction below:

```sql
CREATE TABLE t (
k INT PRIMARY KEY,
i INT
);

SELECT DISTINCT i FROM t ORDER BY i;
-- i
-- -----
-- (0 rows)

SET null_ordered_last = true;

SELECT DISTINCT i FROM t ORDER BY i;
-- ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select list
-- SQLSTATE: 42P10
```

This bug has been present since v22.1.0 when `null_ordered_last` was introduced.

Jira issue: CRDB-57535