[JENKINS-66718] Un-inlining script in BuildTimelineWidget/control.jelly

[megathaum]

See JENKINS-66718.

Proposed changelog entries

• Un-inline script in BuildTimelineWidget/control.jelly to prepare for the introduction of Content Security Policy

Proposed upgrade guidelines

N/A

Submitter checklist

• (If applicable) Jira issue is well described
• Changelog entries and upgrade guidelines are appropriate for the audience affected by the change (users or developer, depending on the change). Examples
  • Fill-in the Proposed changelog entries section only if there are breaking changes or other changes which may require extra steps from users during the upgrade
• Appropriate autotests or explanation to why this change has no tests
• For dependency updates: links to external changelogs and, if possible, full diffs

Desired reviewers

@Wadeck

Maintainer checklist

Before the changes are marked as ready-for-merge:

• There are at least 2 approvals for the pull request and no outstanding requests for change
• Conversations in the pull request are over OR it is explicit that a reviewer does not block the change
• Changelog entries in the PR title and/or Proposed changelog entries are correct
• Proper changelog labels are set so that the changelog can be generated automatically
• If the change needs additional upgrade steps from users, upgrade-guide-needed label is set and there is a Proposed upgrade guidelines section in the PR title. (example)
• If it would make sense to backport the change to LTS, a Jira issue must exist, be a Bug or Improvement, and be labeled as lts-candidate to be considered (see query).

[Wadeck]

Not tested manually but it seems to have nothing wrong there :)

The different variables defined at the top level of the build-timeline-widget.js will be "global", = accessible outside of the script, but as this script is "local" to a single page, the risk of collision is pretty small.

If we are detecting such collision, we can just wrap it with the same kind of structure as it was done at the bottom of the script already 👍

Thanks for the contribution 🐝 🚀

[Wadeck]

Tips: document.getElementById('build-timeline-div') is an alternative (not necessarily faster, but perhaps more readable).
(No change required)

[megathaum]

Thanks. I'll remember it for the next time.

[megathaum]

Thank you @Wadeck for the review. I did a manual test before and after. The timeline widget shows the builds successfully and I didn't see any errors in the console (browser's developer tool).

[timja]

This PR is now ready for merge, after ~24 hours, we will merge it if there's no negative feedback.

Thanks!