Fork java -jar jenkins.war from hpi:run #840
Description
The current implementation of hpi:run which uses Jetty-specific APIs to run Jenkins in-process was always a bad idea, and causes all sorts of maintenance headaches such as #652. It would be better to just set up the desired work/plugins/ but then actually run java -jar jenkins.war using Winstone: jenkinsci/jenkins#9615 (comment)
(My current issue is that it does not properly honor argLine and thus seems to be missing --add-opens java.base/java.io=ALL-UNNAMED, causing problems for Pipeline. #507 does not seem to work on Java 25.)