release-23.1: sql: fix decimal evaluation edge cases

[DrewKimball]

Backport 1/1 commits from #106472.

/cc @cockroachdb/release

---

Previously, the logic for decimal and float division, floor division and mod operators was incorrect for a few edge cases involving NaN or Infinity values. For example, 'NaN'::DECIMAL / 0 would throw a division-by-zero error when it should evaluate to NaN and 0/'inf'::DECIMAL returned 0E-2019 instead of just 0.

This patch updates the special-case logic to mirror that of postgres, so division-by-zero errors always check the NaN case and the division by infinity case returns a 0 without extra digits.

Fixes #40929
Fixes #103633

Release note (bug fix): Fixed edge cases in decimal and float evaluation for division operators. 'NaN'::DECIMAL / 0 will now return NaN instead of a division-by-zero error, and 0 / 'inf'::DECIMAL will return 0 instead of 0E-2019.

Release justification: Fix for a decimal-precision edge case that is causing randomized test failures.

[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 

[yuzefovich]

Did you intentionally omit the removal of the skip in sqlsmith (looks like that is the only difference from #106472)?

Reviewed 14 of 14 files at r1, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @DrewKimball)

[DrewKimball]

Did you intentionally omit the removal of the skip in sqlsmith (looks like that is the only difference from #106472)?

No, thanks for catching that.

[yuzefovich]

Approving assuming you'll remove the skip before merging (although that might invalidate the approval).

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @DrewKimball)