release-21.1: sql: add internal tables cross db refs and interleaved indexes/tables

[fqazi]

Backport 1/1 commits from #61629.

/cc @cockroachdb/release

Release Justification: This backport introduces new crdb_internal functions that allow users to detect
if they have interleaved tables or cross-database references. The changes themselves are low
risk and make it easier to migrate away from these features.

---

Fixes: #58867

Previously, users had no way of determining which objects in
their database utilized either deprecated features like
interleaved indexes/tables or cross DB references. This was
inadequate since users need to know which object utilize
this functionality. To address this, this patch introduces
the crdb_internal tables: cross_db_references, interleaved_indexes,
interleaved_tables.

Release justification: Low risk internal tables for detecting
deprecated features.
Release note (sql change): Added crdb_internal tables cross_db_references,
interleaved_indexes, and interleaved_tables for detecting the
deprecated features cross db references and interleaved tables
/ indexes within a given database.

[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 

[ajwerner]

Reviewed 14 of 15 files at r1, 1 of 1 files at r2, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @fqazi)