release-23.1: storage: fix comparison of suffixes

[RaduBerinde]

Backport 1/1 commits from #129739.

/cc @cockroachdb/release

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Backport 1/1 commits from #129605 on behalf of @RaduBerinde.

/cc @cockroachdb/release

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This is a partial backport of #128043. CC @cockroachdb/release

Release justification: this fixes an issue hit in a real cluster where
a range key is never cleaned up.

The EngineComparer has a bug when comparing bare suffixes - we call
the normalization function on a slice without the sentinel byte; that
function's logic is based on length so it will not function properly.

We recently observed that this can cause problems when a
RangeKeySet has a suffix with the (now obsolete) synthetic bit set,
and the corresponding RangeKeyUnset is issued by a newer version and
doesn't have the bit set. These suffixes are supposed to equal each
other but this is not currently the case.

We fix the comparator to account for this case correctly and add a
more comprehensive test. On the old code, the updated test failed
with:

Compare(0000000000000002000000010d, 000000000000000200000001010e) = 1, expected 0

Fixes: #129592
Release note: None

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Release justification:

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Backports should only be created for serious
  issues or test-only changes.
• Backports should not break backwards-compatibility.
• Backports should change as little code as possible.
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• Backports should not add new functionality (except as defined
  here).
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• All backports must be reviewed by the owning areas TL. For more information as to how that review should be conducted, please consult the backport
  policy.

If your backport adds new functionality, please ensure that the following additional criteria are satisfied:

• 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. State changes must be further protected such that nodes running old binaries will not be negatively impacted by the new state (with a mixed version test added).
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  channel (#db-backports-point-releases or #db-backports-XX-X-release) for awareness and discussion.

Also, please add a brief release justification to the body of your PR to justify this
backport.

[cockroach-teamcity]

This change is 

[RaduBerinde]

pkg/storage/pebble.go line 148 at r1 (raw file):

	// Empty suffixes come before non-empty suffixes.
	if aSuffixLen == 0 {

Had to make a change here since cmp.Compare is not available on this branch.

[jbowens]

Reviewed 1 of 1 files at r2.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @nicktrav and @RaduBerinde)

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pkg/storage/pebble.go line 148 at r1 (raw file):

Previously, RaduBerinde wrote…

Had to make a change here since cmp.Compare is not available on this branch.

change lgtm