release-23.1: sql/catalog: avoid fetching descriptors when fetching comments

[blathers-crl]

Backport 2/2 commits from #103106 on behalf of @fqazi.

/cc @cockroachdb/release

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Previously, we refactored the code to fetch comments, descriptors, and zone config together in all cases. A side effect of this change was that the crdb_internal.kv_system_comments table was substantially slower for larger tables leading to big regressions. To address this, this patch adds a method of only fetching comments within the collections.

Additionally, we added many builtins into both functions, which meant our existing virtual index look-up could end up falling back too frequently to full scans. Also, a virtual index is added on the kv_catalog_comments table for fast point look-ups when referencing descriptors.

Informs: #102851
Fixes: #102613

Release note (bug fix): Optimize over-head of
pg_catalog.pg_description and pg_catalog.pg_shdescription, which can lead to performance regression relative to 22.2

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Release justification: necessary performance enhancement

[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 

[fqazi]

@rafiss This is expected. That query ends up trying to do a GET for each builtin into the descriptors table, so it's a different in builtin counts (there's a delta of 2 between master and 23.1).