Pathauto support

The update code of an already imported entity is:

           foreach ($entity_data['attributes'] as $field_name => $value) {
              $field_name = $resource_type->getInternalName($field_name);
              $existing_translation->set(
                $field_name,
                $entity->get($field_name)->getValue()
              );
            }

            $translation = $entity->toArray();
            $existing_entity->addTranslation($data_langcode, $translation);
            $existing_entity->save();
            $existing_translation = $existing_entity->getTranslation($data_langcode);

Maybe due to that, as the path is a calculated value, the addition of the "pathauto" data has no impact.

Also, maybe with #2336597: Convert path aliases to full featured entities, this will be solved automatically. Needs to test when path alias are entities if it will be ok.

Here is a patch that adds an field enhancer to allow to expose pathauto state.

See automated tests for the behavior.

Also, I won't be able to commit the patch (at least the tests) because of deprecation warnings in Pathauto.

Merged.

Tests separated in a dedicated issue: #3089850: Tests: Pathauto support