Support Drupal Symfony Mailer for HTML

Problem/Motivation

The config page (/admin/config/mass-contact/settings/body) does not allow to configure HTML settings as it requires Mime Mail or Swiftmailer. But Drupal Symfony Mailer → is a replacement of Swiftmailer and should be supported, too.

Steps to reproduce

Open /admin/config/mass-contact/settings/body when Drupal Symfony Mailer is installed.

Proposed resolution

Add Drupal Symfony Mailer to the list of supported modules.