release-22.2.0: opt: don't add reordered join with extra filters to original memo group

[blathers-crl]

Backport 1/1 commits from #88779 on behalf of @DrewKimball.

/cc @cockroachdb/release

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The JoinOrderBuilder builds reordered join plans from the bottom up.
It expects filters to be pushed down as far as possible at each step, and
that transitive closure has been calculated over Inner Join equality filters
(e.g. a=b and b=c => a=c). It also reuses the original matched joins
when possible to avoid duplicate work by adding to the original memo groups.

This could previously cause filters to be dropped in the case when the
original join tree did not compute transitive closure and push filters down
as far as possible. More specifically, the JoinOrderBuilder could add new
reordered joins with new filters synthesized and pushed down as far as possible
to an original memo group that didn't have one of those filters. Subsequent
joins would then expect the filter to be part of the memo group, and so it
wouldn't be added later on in the plan. In the rare case when the expression
without the filter was chosen, this could manifest as a dropped filter in the
final plan. This was rare because dropping a filter usually does not produce
a lower-cost plan.

As an example, take this original join tree:

(xy join ab on true) join uv on x = u and a = u;

Here it is possible to sythesize and push down a x = a filter, and so the
JoinOrderBuilder would do this and add it to the group:

group (xy join ab on true), (xy join ab on x = a)

Later joins would use this group as an input, an expect the x = a filter to
be present. If costing happened to choose the first expression in the group,
we would end up choosing a plan like this:

(xy join ab on true) join uv on x = u

Where the a = u filter isn't included in the top-level join because it
would be redundant to add it when x = u and x = a are already present.
This is a bit of a simplification, but is essentially the problem fixed
by this commit.

This commit adds a check to the JoinOrderBuilder to identify cases where
filters (including ones sythesized from the transitive closure) weren't
pushed all the way down in the original join tree. When this is true, none
of the originally matched joins can be reused when reordered joins are
built except for the root join. This solution may perform some duplicate
work when filters aren't pushed down, but it shouldn't matter because this
case is rare (and should be avoided whenever possible).

Fixes #88659

Release note (bug fix): Fixed a bug introduced in 20.2 that could cause
filters to be dropped from a query plan with many joins in rare cases.

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Release justification: low-risk fix for rare optimizer correctness bug

[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 

[mgartner]

LGTM

[DrewKimball]

TFTR!