Use #process in CommentWidget::formElement

Problem/Motivation

This is a follow up to #394374: Participant had difficulty understanding the concept behind "read only" commenting. That was committed and then re-opened for cleanup in #394374-50: Participant had difficulty understanding the concept behind "read only" commenting.

It's really bad form to expand the radios ourselves. That's why we have #process! :) Here's a FAPI cleanup for adding the options to the comment settings radios. The plus side is we can also apply the descriptions to the content type settings as well now.

This is for \Drupal\comment\Plugin\Field\FieldWidget\CommentWidget::formElement

Steps to reproduce

Proposed resolution

Remaining tasks

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Introduced terminology

API changes

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Release notes snippet