[JENKINS-60866] Extract inline JS from progressive rendering

[daniel-beck]

See JENKINS-60866.

Right now I am feeling pretty good about our ability to make st:bind CSP-compliant in a compatible way (that ended up in #6865). This PR just extracts inline JS from progressiveRendering that is defined there directly.

This tag is used e.g. for /asynchPeople/.

I checked whether any callbacks exist that aren't just function names via GH search and did not find any (but that's not a thorough search).

The chosen approach should be compatible with pages having multiple progressiveRendering, but not with AJAX supplied progressiveRendering (which I doubt exist, but cannot be sure). Please let me know if this should be done with Behavior instead.

Proposed changelog entries

Too minor (unless we count the redefinition of the argument)

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) and are in the imperative mood. 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
• New public classes, fields, and methods are annotated with @Restricted or have @since TODO Javadoc, as appropriate.
• New deprecations are annotated with @Deprecated(since = "TODO") or @Deprecated(forRemoval = true, since = "TODO") if applicable.
• For dependency updates: links to external changelogs and, if possible, full diffs

Desired reviewers

@mention

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 accurate, human-readable, and in the imperative mood
• 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).

[NotMyFault]

Provisionally approving if Tim's suggestions are addressed.

[daniel-beck]

Thanks everyone!

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