[Drupal 9] Webform::url, Webform::urlInfo() and Webform::link() method call fails

So thanks for the fast work on this one, but I don't think the fix is correct.

For example, the url method has been changed to merely return the value of toUrl but the return type of the former is a string, whereas the return type of the latter is \Drupal\Core\Url

I think you want the code from Drupal 8.9 core, so it should look like:

public function url($rel = 'canonical', $options = []) {
  @trigger_error('EntityInterface::url() is deprecated in Drupal 8.0.0 and will be removed in Drupal 9.0.0. EntityInterface::toUrl() instead. Note, a \\Drupal\\Core\\Url object is returned. See https://www.drupal.org/node/2614344', E_USER_DEPRECATED);

  // While self::toUrl() will throw an exception if the entity has no id,
  // the expected result for a URL is always a string.
  if ($this
    ->id() === NULL || !$this
    ->hasLinkTemplate($rel)) {
    return '';
  }
  $uri = $this
    ->toUrl($rel);
  $options += $uri
    ->getOptions();
  $uri
    ->setOptions($options);
  return $uri
    ->toString();
}

But equally the deprecation notice should probably reference the next version of Webform, rather than Drupal core?

The other methods might have similar issues, I've not checked, sorry.

Looks better, thanks!