release-23.1: sql: fix record-returning udfs when used as data source

[rharding6373]

Backport 1/1 commits from #98162.

/cc @cockroachdb/release

---

When record-returning UDFs (both implicit and RECORD return types) are used as a data source in a query, the result should be treated as a row with separate columns instead of a tuple, which is how UDF output is normally treated. This PR closes this gap between CRDB and Postgres.

For example:

CREATE FUNCTION f() RETURNS RECORD AS
$$
  SELECT 1, 2, 3;
$$ LANGUAGE SQL

SELECT f()
    f
--------
 (1,2,3)

SELECT * FROM f() as foo(a int, b int, c int);
 a | b | c
---+---+---
 1 | 2 | 3

The behavior is the same for implicit record return types.

Epic: CRDB-19496
Fixes: #97059

Release note: None

Release justification: Fixes a bug in how UDFs are handled when used as a data source.

[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 

[rharding6373]

Gentle ping @mgartner

[mgartner]

Apologies for the delay. LGTM.

[rharding6373]

TFTR!