[V4] Provide the ability to produce "entity_url" as an absolute URL

[rollki]

It seems there's no way to get entity URL via entity_url data producer as an absolute URL object.
Probably we can add an optional consumes to that producer.

So, to produce an absolute URL we can do something like:

    $registry->addFieldResolver('Topic', 'url',
      $builder->compose(
        $builder->produce('entity_url')
          ->map('entity', $builder->fromParent())
          ->map('absolute', $builder->fromValue(TRUE)),
        $builder->produce('url_path')
          ->map('url', $builder->fromParent())
      )
    );

[klausi]

Merged in #1291, thanks for reporting!