Add test coverage for rich text props in page variant config translation

Problem

Translating a page region that contained a rich text prop (e.g. the Haven footer) crashed with Call to a member function getValue() on null. CKEditor 5's widget alter needs a host entity, and config translation didn't provide one.

Current state

This no longer happens on 1.x. Page regions were replaced by page variants (#3591806 (closed)), and PageVariant provides a host entity through EmptyTargetEntityProviderInterface. The existing testPageVariantTranslation() covers only plain text and link props, so nothing guards against a regression.

Proposed resolution

Extend ConfigWithComponentTreeConfigTranslationUiTest with a rich text prop. It checks that the translation form renders and that the translated HTML is saved (MR !1526).

Original report
  1. Install Drupal CMS with Haven.
  2. Enable configuration translation and add a language.
  3. Translate the Footer → fatal error in Ckeditor5Hooks::fieldWidgetSingleElementFormAlter() via CanvasStaticPropSourceFieldWidget::buildWidgetForm().
Edited by drupalbot