Make helper functions in ckeditor.js available outside the IIFE

Problem/Motivation

In this experience builder issue, we added support for running Drupal's CKEditor 5 integration in React #3484395: CKEditor 5 not loading on formatted text Field Widgets in the component instance form.

This required pasting in most of the helper functions from ckeditor5.js, which means it's super-not-DRY and there's a risk of them going out of sync.

There's also not much risk in just making these available somewhere in a Global object, so perhaps we could do that and it would benefit Experience Builder and other projects that would like a higher degree of control over CKEditor5 integration while still largely adhering to how core does it.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet