[JENKINS-73156] handle svg cleanup of symbols via an xml document

[mawinter69]

some attributes and elements where removed via regular expressions that removed more than what is necessary. Additionally stroke:#000 was replaced with currentColor because there are some icons that still use that.
This had side-effects when symbols are used that are not just black/white, e.g. using svgs from jenkins artwork via customizable-header plugin. There are constructs like using class attributes and a style definition referring to the classes. At other places there where color definitions with stroke:#000abc which were incorrectly modified.

svg cleanup is now implemented with DOM manipulation which is more robust.
5 icons that still used stroke:#000 are converted to use stroke:currentColor

opened jenkinsci/ionicons-api-plugin#64 as followup to fix some occurrences of stroke:#000

See JENKINS-73156.

Testing done

Manual testing, that the changed icons still work properly with dark theme.
Used some of the SVGs from https://www.jenkins.io/artwork/ and provided them as symbol in customizable-header plugin and verified they are properly shown

Proposed changelog entries

• Handle svg cleanup via an xml document to avoid broken symbols.

Proposed upgrade guidelines

update ionicons-api plugin to at least version 74.v93d5eb_813d5f

Submitter checklist

Beta Give feedback

1. The Jira issue, if it exists, is well-described.
2. The changelog entries and upgrade guidelines are appropriate for the audience affected by the change (users or developers, depending on the change) and are in the imperative mood (see examples). Fill in the Proposed upgrade guidelines section only if there are breaking changes or changes that may require extra steps from users during upgrade.
3. There is automated testing or an explanation as to why this change has no tests.
4. New public classes, fields, and methods are annotated with @Restricted or have @since TODO Javadocs, as appropriate.
5. New deprecations are annotated with @Deprecated(since = "TODO") or @Deprecated(forRemoval = true, since = "TODO"), if applicable.
6. New or substantially changed JavaScript is not defined inline and does not call eval to ease future introduction of Content Security Policy (CSP) directives (see documentation).
7. For dependency updates, there are links to external changelogs and, if possible, full differentials.
8. For new APIs and extension points, there is a link to at least one consumer.

Desired reviewers

@mention

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

Maintainer checklist

Beta Give feedback

1. There are at least two (2) approvals for the pull request and no outstanding requests for change.
2. Conversations in the pull request are over, or it is explicit that a reviewer is not blocking the change.
3. Changelog entries in the pull request title and/or Proposed changelog entries are accurate, human-readable, and in the imperative mood.
4. Proper changelog labels are set so that the changelog can be generated automatically.
5. If the change needs additional upgrade steps from users, the upgrade-guide-needed label is set and there is a Proposed upgrade guidelines section in the pull request title (see example).
6. 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).

[mawinter69]

As before just emptying the title elements. But why not just delete them completely?

[NotMyFault]

/label ready-for-merge

---

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