release-23.1: opt: fixup CTE stats on placeholder queries

[blathers-crl]

Backport 1/1 commits from #99433 on behalf of @cucaroach.

/cc @cockroachdb/release

---

During optbuilder phase we copy the initial expressions stats into the
fake-rel but this value can change when placeholders are assigned so add
code in AssignPlaceholders to rebuild the cte if the stats change.

Fixes: #99389
Epic: none
Release note: none

---

Release justification: Fixes issue with chosing optimal plan when using placeholders with CTE queries where only workaround was to not use placeholders.

[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]

Let's hold off on merging this until v23.1.1. I've added the do-not-merge label for now.

[cucaroach]

Should I wait to do 22.2 and 22.1 as well or is it fine for fixes to get backported to older releases before newer releases? Seems weird but probably benign.

[mgartner]

We can backport to 22.2 and 22.1 now. For 23.1 we're only merging blockers at the moment.

[github-actions]

Reminder: it has been 3 weeks please merge or close your backport!

[cucaroach]

Removed DNM label, ready to go into 23.1 now.

[mgartner]

Don't forget to add a release-justification.

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @cucaroach, @DrewKimball, @msirek, and @rharding6373)