opt: fix incorrect column indexing in index recommendations

[mgartner]

opt: fix incorrect column indexing in index recommendations

Fixes #83965

Release note (bug fix): A minor bug has been fixed that caused internal
errors and poor index recommendations when running EXPLAIN statements.

opt: clarify logic in Metadata.UpdateTableMeta

Release note: None

[cockroach-teamcity]

This change is 

[msirek]

Reviewed 3 of 3 files at r1, 1 of 1 files at r2, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @rytaft and @wenyihu6)

[mgartner]

TFTR!

bors r+

[mgartner]

bors r+

[craig]

Build succeeded:

• GitHub CI (Cockroach)

[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

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error creating merge commit from f678273 to blathers/backport-release-22.1-84169: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 22.1.x failed. See errors above.

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