This patch bumps the actions script version in the issue-write workflow
to v7. This was done before but rolled back due to errors as there were
breaking changes in v5
(https://github.com/actions/github-script#breaking-changes-in-v5). This
was reverted in f984b47.

This patch makes the necessary changes to prevent job failures.

Fixes #130211.

This patch reverts that upgrade which was performed in
74df2032d467618a9aab085120539e306f21bcc0. This broke the workflow, presumably
due to the breaking changes introduced in v5 of this action.

This is a stop-gap for #130211.

This patch replaces all instances of ubuntu-latest with ubuntu-24.04
(outside of the entries in libc++) based on the guidelines in the LLVM
CI best practices doc (https://llvm.org/docs/CIBestPractices.html).

These two actions are particularly old, and should be updated to the
latest version. Doing this in a specific commit to easily roll back if
things break and to get as much testing done as possible within the jobs
triggered as a part of these changes.

This patch haspins all actions in most of the LLVM Github workflows.
This is something we try to do, but no one has gone through and combed
through all of the workflows before this patch.

Notably, this patch does not bump any major versions of actions just in
case there are subtle breaking changes introduced between versions that
could impact us. Also, this patch omits the libc/libc++ workflows so
that they can be split into separate PRs for the respective subproject
maintainers to review.

This adds a new composite workflow that allows you to download artifacts
from other workflows without using an access token.

actions/download-artifact from GitHub requires an access token in order
to download artifacts from a different workflow, which is why we can't
use it here if we want to avoid using a token.

See
https://github.com/actions/download-artifact?tab=readme-ov-file#download-artifacts-from-other-workflow-runs-or-repositories

This patch makes the issue write workflow only run after success or
failure of the workflow invoking it, preventing it from running where
the original workflow was skipped.

Fixes #97294

We need to use the issue-write workflow to write the comments, because
pull_request targets don't have permissions to write comments.

This allows us to use the less privileged pull_request event for the
validate_email job, since this workflow no longer writes a comment
directly.

Fixes #87102 .