release-22.2: opt: fix internal error when exploration uncovers null-rejection

[blathers-crl]

Backport 1/1 commits from #100565 on behalf of @DrewKimball.

/cc @cockroachdb/release

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It is possible for exploration rules to reveal opportunities to null-reject (simplify) an outer join that were not visible during normalization. Previously, this would cause an internal error, since it was assumed null-rejection would never be requested by an expression that can prove the requested column is non-null. This patch removes the assertion and instead removes any proven non-null columns from the requested null-rejection column set. Note that this solution is orthogonal to improving null-rejection during normalization - one instance of this is tracked in #100564.

Fixes #100559

Release note (bug fix): Fixed a bug existing since before 22.1 that could cause an internal error in rare cases for a query with outer joins that can be simplified to non-outer joins and at least one semi-join.

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Release justification: low-risk fix for optimizer internal error

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is 

[msirek]

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @DrewKimball and @mgartner)