sql/sem: add support for "pg_blocking_pids" builtin

[girishv-tw]

added support pg_blocking_pids builtin. Needed for pgadmin.

Closes #91068

Release note (sql change): add support for pg_blocking_pids builtin function. It is hardcoded to return an empty array because CockroachDB has no equivalent concept of PIDs as in Postgres.

[cockroach-teamcity]

All committers have signed the CLA.

[blathers-crl]

Thank you for contributing to CockroachDB. Please ensure you have followed the guidelines for creating a PR.

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I have added a few people who may be able to assist in reviewing:

• @jordanlewis (author of pgbuiltins: pg_blocking_pids #91068)

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[cockroach-teamcity]

This change is 

[jordanlewis]

Thanks @girishv-tw! There are some test failures:

  panic: Missing an entry for pg_blocking_pids() -> int[] in builtins.BuiltinOidsBySignature. Update the signature there if it's changed, or if it's new, add the following entry:`pg_blocking_pids() -> int[]`: 2045

Try to update that and resubmit.

[blathers-crl]

Thank you for updating your pull request.

Before a member of our team reviews your PR, I have some potential action items for you:

• We notice you have more than one commit in your PR. We try break logical changes into separate commits, but commits such as "fix typo" or "address review commits" should be squashed into one commit and pushed with --force
• Please ensure your git commit message contains a release note.
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[girishv-tw]

@jordanlewis , thanks for pointing that out . I have made the necessary changes and it looks like the tests are passing now.

[jordanlewis]

Looks good! If you could squash your commits into one, we'll be ready to merge. Thanks.

[rafiss]

i took care of squashing the commits. thanks for your contribution!

bors r+

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)