release-24.1: backup: capture function descriptor changes in revision history backups

[msbutler]

Backport 1/1 commits from #156634.

/cc @cockroachdb/release

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Previously, backup would omit grabbing a function descriptor in revision history backups if the function did not exist at the end time or only within the interval. This patch fixes this bug.

Fixes #156206

Release note: none

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that it falls into one of the following categories (select one):

• Non-production code changes. Includes test-only changes, build system changes, etc.
• Fixes for serious issues. Defined in the policy as correctness, stability, or security issues, data corruption/loss, significant performance regressions, breaking working and widely used functionality, or an inability to detect and debug production issues.
• Other approved changes. These changes must be gated behind a disabled-by-default feature flag unless there is a strong justification not to.

Add a brief release justification to the PR description explaining your selection.

Also, confirm that the change does not break backward compatibility and complies with all aspects of the backport policy.

All backports must be reviewed by the TL and EM for the owning area.

[cockroach-teamcity]

This change is 

[blathers-crl]

❌ PR #156663 does not comply with backport policy

Confidence: high
Explanation: The pull request appears to address a function descriptor omission bug during revision history backups, which could potentially cause inaccurate restoration data if these descriptors are not recorded correctly. However, the PR does not specifically justify that the bug fixed is a 'critical bug' under the policy's given categories (like data corruption/loss or result in suboptimal performance explicitly), nor does it implement feature flag gating. The PR's changes are also not limited strictly to non-production files, as modified files include pkg/ccl/backupccl/backupinfo/manifest_handling.go and pkg/ccl/backupccl/targets.go, which are part of the production code. There is no 'Release justification:' line in the PR body that meets the criteria for exemption. Despite describing this bug, it does not frame it as critical per se, nor does the bug appear to directly fit under the listed critical bug criteria fully.
Recommendation: Request clarification for how the bug is considered critical under policy specified criteria, or suggest gating the changes behind a feature flag.

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