release-22.1: opt: fix invalid transformation in SplitLimitedSelectIntoUnionSelects

[mgartner]

Backport 1/1 commits from #89113.

/cc @cockroachdb/release

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opt: fix invalid transformation in SplitLimitedSelectIntoUnionSelects

This commit removes some untested logic in
SplitLimitedSelectIntoUnionSelects that created invalid expression
transformations. With this logic, this rule could construct an unordered
limit below the UnionAll which is incorrect. The bug could cause
incorrect query results.

Fixes #88993

Release note (bug fix): A bug has been fixed that could cause incorrect
results in rare cases. The bug could only present if the following
conditions were true:

1. A query with ORDER BY and LIMIT was executed.
2. The table containing the ORDER BY columns had an index containing
   those columns.
3. The index in (2) contained a prefix of columns held to a fixed
   number of values by the query filter (e.g., WHERE a IN (1, 3)),
   a CHECK constraint (e.g., CHECK (a IN (1, 3))), inferred by
   a computed column expression (e.g. WHERE a IN (1, 3) and a column
   b INT AS (a + 10) STORED), or inferred by a PARTITION BY clause
   (e.g. INDEX (a, ...) PARTITION BY LIST (a) (PARTITION p VALUES ((1), (3)))).
   This bug was present since version 22.1.0.

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Release justification: Correctness bug fix.

[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 

[rytaft]

Reviewed 5 of 5 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @msirek)