release-24.1: plpgsql: add support for CALL statements

[blathers-crl]

Backport 3/3 commits from #121319 on behalf of @DrewKimball.

/cc @cockroachdb/release

---

opt/optbuilder: reset builder context for nested routines

This commit resets the Builder.insideDataSource field in the optbuilder
when building the body of a routine. This is necessary since a nested
routine is not (necessarily) inside a data source, even if its parent it.

Fixes #121316

Release note: None

plpgsql/parser: add parser support for CALL statements

This commit adds support in the PL/pgSQL parser for CALL statements
within a PL/pgSQL routine.

Informs #120818

Release note: None

plpgsql: implement CALL statements

This commit adds support for the PL/pgSQL CALL statement. This allows
a PL/pgSQL routine to execute a stored procedure. Note that there is
a behavior difference vs SQL CALL statements: if the stored procedure
has OUT parameters, the surrounding routine passes variables in each
OUT parameter position, and the result of the procedure is assigned to
those variables.

Fixes #120818

Release note (sql change): Added support for PL/pgSQL CALL statements.
It is now possible to call a stored procedure from a PL/pgSQL routine.

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Release justification: low-risk new functionality

[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.
• Backports should not change on-disk formats or node communication protocols.
• Backports should not add new functionality (except as defined
  here).
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• All backports must be reviewed by the owning areas TL and one additional
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  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).
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.
• Your backport must be accompanied by a post to the appropriate Slack
  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.

[blathers-crl]

Your pull request contains more than 1000 changes. It is strongly encouraged to split big PRs into smaller chunks.

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[yuzefovich]

Reviewed 3 of 3 files at r1, 4 of 4 files at r2, 23 of 23 files at r3, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @DrewKimball, @mgartner, and @stevendanna)

[mgartner]

Reviewed 3 of 3 files at r1, 4 of 4 files at r2, 23 of 23 files at r3, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @DrewKimball and @stevendanna)

[yuzefovich]

Merging so that I can backport on top if it.