Render the popup with a template

Rerolled original patch to apply to latest version of the module (3.0.3).

I confirm that the patch works correctly with module version 3.0.3 and Drupal Core 10.4.7. Thanks.

I'm using this patch on a Drupal 11.1.7 website (Popup message version 3.0.3) and it's working great!

I think it's necessary to override the template, especially to:

• Add a role="dialog" for accessibility
• Change the h1 to a h2 or h3. Having an h1 on the dialog is a bad idea for SEO