Handle multiple forms in one form decorator

For those cases it is possible to implement the applies method like this:

  /**
   * {@inheritdoc}
   */
  public function applies(): bool {
    return
      in_array('form_group_type_edit_form_alter', $this->getHooks($this->inner), TRUE)
      || in_array('form_group_type_add_form_alter', $this->getHooks($this->inner), TRUE);
  }

This working example shows how to alter the group edit and group add form at the same time.