Jenkins relies on https://github.com/stapler/stapler-adjunct-codemirror to utilize code mirror.
This library is almost 10 years out of date and ships an ancient version of codemirror 2 (6 is the newest while writing this)

Modern and maintained versions of codemirror continue to exist as NPM packages: https://www.npmjs.com/package/codemirror?activeTab=dependencies, we can utilize in the war/ module.

Core defines only two usages of this library:

• https://github.com/jenkinsci/jenkins/blob/5753749dc6d4255d9e915fedd8591c02510436bd/core/src/main/resources/lib/hudson/scriptConsole.jelly#L54-L55
• https://github.com/jenkinsci/jenkins/blob/5753749dc6d4255d9e915fedd8591c02510436bd/core/src/main/resources/lib/form/textarea.jelly#L86-L90

and there are no direct dependencies in plugins: https://github.com/search?q=org%3Ajenkinsci+%22stapler-adjunct-codemirror%22+lang%3A%22Maven+POM%22&type=code