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[bot]]

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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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.
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[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.