release-23.2: kvcoord: fix error index in case of range split

[blathers-crl]

Backport 1/1 commits from #113111 on behalf of @yuzefovich.

/cc @cockroachdb/release

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This commit fixes the DistSender to set the correct error index in case an error is encountered after divideAndSendBatchToRanges was called recursively due to a stale range cache. In this scenario, previously we would have the error index set as if the original batch was the one right before the recursive call, which is incorrect in case that batch itself was split (e.g. because the original batch touched multiple ranges, and each sub-batch was executed in parallel). We already had the error index mapping code in place for the main code path, but we forgot to do the error index re-mapping after two recursive calls, which is now fixed.

This commit additionally pulls out the logic to set response.positions out of sendPartialBatch since there are fewer places to do that one level up.

This bug has been present for a very long time, but it seems relatively minor, so I decided to not include the release note.

Fixes: #111481.

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 

[yuzefovich]

Friendly ping @nvanbenschoten