Use Unicode escapes when properties files are both valid UTF-8 and ISO-8859-1

[timja]

See jenkinsci/stapler#357
and #6546 (comment)

Ran with https://gist.github.com/timja/21d655840f5d617df07a271a7db0a48f

and then paths outputted to a file and native2ascii used over top:

cat /tmp/files.txt | xargs -I {} -n 1 bash -c "native2ascii {} > /tmp/ascii.txt && mv /tmp/ascii.txt {}"

Proposed changelog entries

• Correct encoding for several localized strings.

Proposed upgrade guidelines

N/A

Submitter checklist

• (If applicable) Jira issue is well described
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• 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
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[basil]

I just merged a different localization PR so it would be nice to confirm that there are no conflicts.

[basil]

This PR is now ready for merge. We will merge it after approximately 24 hours if there is no negative feedback. Please see the merge process documentation for more information about the merge process. Thanks!

[basil]

As far as I can tell, this should be labelled bug and not skip-changelog, because it contains changes to Messages*.properties, which are handled by this code which is already using PropertyResourceBundle (i.e., presumably already showing mojibake when running on Java 9+).

[basil]

In fact #6382 seems to have been an attempt to address one symptom of this problem, but the fix was incomplete. This PR eradicates the problem.

[timja]

I just merged a different localization PR so it would be nice to confirm that there are no conflicts.

No new issues from merging master locally

[jglick]

Worth adding to

jenkins/test/src/test/java/jenkins/CorePropertiesTest.java

Line 34 in 0f90eba

* Runs checks on properties files in core.

to prevent accidental regression?

[timja]

Done: jenkinsci/jenkins-test-harness#433