Add support for the ProcessedText element

Thanks for the review! In the original implementation I was using RendererInterface::renderInIsolation() but this fails on Drupal 10.2 and I had to switch to the deprecated method (ref commit 981df89).

In December when Drupal 10.2 is EOL we can update the deprecated code.

Automatically closed - issue fixed for 2 weeks with no activity.