Switch to Modal window to allow more editor control

Problem/Motivation

The custom editor is limited in what it offers in terms of customising the editor experience, such as:

• Ability to add links, bold, underline within the editor
• Ability to add field descriptions within the editor such as explaining that automated numbering is in place if left blank

How it currently looks:

Proposed resolution

Suggest we switch to Drupal's modal window like https://www.drupal.org/project/ckeditor5_embedded_content does. Here is a proof of concept screenshot implemented in the way that module does, but as an inline object instead. Before considering refining this into a merge request, would like to gauge whether there is even appetite for this or whether I should create it as a separate module (would rather contribute to this module of course!).

Remaining tasks

Provide merge request.

User interface changes

Use Drupal Modal dialogue window.

API changes

None

Data model changes

None, batch update hook to maintain status quo.