Drupal 11 compatibility fixes for Webform Worflows Element

I had to drop support for webform_group_extended → that doesn't seem to be maintained anymore.

All green 🎉

@maxwellkeeble tested locally with a simple Maestro workflow: seems to work fine.

I think we should create a new major version to avoid impacting existing users, the update is quite big.

We are not in a hurry to publish it as the Drupal 11 compatible Webform version has not been released yet.

Webform 6.3.x development branch is now officially compatible with Drupal 11.