Confirmation message for webform submission should be rendered with basic content component.

Problem/Motivation

Confirmation messages from webform submissions are not styled using CivicTheme components.

Steps to reproduce

1. Create a web form
2. Create a confirmation message on submission
3. Submit web form

Proposed resolution

1. Add preprocess for `webform_html_editor_markup` - and preprocess as if its a WYSIWYG field to add CT classes.