release-23.2: rowexec: fix oid handling in merge join and zigzag join

[blathers-crl]

Backport 1/1 commits from #123486 on behalf of @yuzefovich.

/cc @cockroachdb/release

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This commit is a follow up fix to a4b6234 which fixed how we handle zero value Oid types. In particular, we now need to have the precise type information for Oid type family to display zero Oid correctly. Previously, we could have imprecise information in merge join and zigzag joins that was stored in the right-hand side EncDatum when it was decoded using the LHS type, and this is now fixed. I don't think other join types (hash join and lookup join) are susceptible to this since they do decoding at different points in time, so it's unlikely we'd get a similar mix up there.

There is no release note since it seems like an edge case (comparing Oid types with different Oids in non-default row-by-row engine).

Fixes: #123474.

Release note: None

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Release justification: bug fix.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

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[cockroach-teamcity]

This change is 

[DrewKimball]

Reviewed 4 of 4 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @rytaft and @yuzefovich)

[mgartner]

Can you post to backports channel?