release-22.1: release-22.2: only check for introduced spans for online tables in restore

[msbutler]

Backport 1/2 commits from #89102.

/cc @cockroachdb/release

This small patch refines the introduced span corruption checker to
ensure that only online tables in a given backup are checked, as oppose to
all tables included in manifest.Descriptors. This is necessary for checking
cluster backups which currently include offline descriptors in
manifest.Descriptors, which should not be checked, as they will not get
restored. If the table was online at some point in the backup's interval,
the check on each DescriptorChange that brought the table online already covers
this case.

Release note (bug fix): refnes a check conducted during restore that ensures
that all previously offline tables were properly introduced.

Release justification: bug fix

[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 

[stevendanna]

Overall the code looks good. The commit message could be cleaned up a bit, looks like you may have been going in two different directions with a sentence or two and they ended up a little mangled.

Can we add a test for this case?

[msbutler]

good callout. thanks for the proofread :)

added a little test case as well.