release-24.1: opt: disallow non-standard NULL ordering with subqueries in test builds

[blathers-crl]

Backport 1/1 commits from #131254 on behalf of @mgartner.

/cc @cockroachdb/release

---

The optimizer does not correctly build ORDER BY expressions with
non-standard NULL orderings when one or more of the ordering columns
is a projection containing a subquery. This causes test-only assertions
to fail in randomized tests. It is not yet known if there are any issues
with the results of these queries in production builds where the test
assertions are disabled.

For now, we simply return an "unimplemented" error to silence the
failures.

Informs #129956

Release note: None

---

Release justification: Test-only change.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Backports should only be created for serious
  issues or test-only changes.
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[cockroach-teamcity]

This change is 

[yuzefovich]

Backporting to prevent creation of duplicates of #129956 on 24.1 branch.

[yuzefovich]

Reviewed 4 of 4 files at r1, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @DrewKimball and @mgartner)