release-23.1: kv: wait on latches on each key in reverse acquisition order

[blathers-crl]

Backport 1/1 commits from #109349 on behalf of @nvanbenschoten.

/cc @cockroachdb/release

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This commit allocates latch IDs from the top of the uint64 space and in reverse order. This is done to order latches in the tree on the same key in reverse order of acquisition. Doing so ensures that when we iterate over the tree and see a key with many conflicting latches, we visit the latches on that key in the reverse order that they will be released. In doing so, we minimize the number of open channels that we wait on (calls to waitForSignal) and minimize the number of goroutine scheduling points. This is important to avoid spikes in runnable goroutine after each request completes, which can negatively affect node health.

See experiments below.

Epic: None
Release note (performance improvement): The impact of high concurrency blind writes to the same key on goroutine scheduling latency was reduced.

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Release justification: small performance and stability improvement.

[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?

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[arulajmani]

Stamping the backport, but let's let this bake on master for a few weeks like you mentioned in your original PR.