Allow entity reference values to be ids.

[aronbeal]

The expand function in the existing version of the D7 entity reference handler makes the assumption that the argument that is passed in will be a title string (or a name, in the case of the user). I suggest the following modification, which makes the assumption that the argument is a nid (or uid) if the $value is numeric.

I can't test the D8 version I cooked up, but I'm guessing it would look like something like the following:

  /**
   * {@inheritdoc}
   */
  public function expand($values) {
    $return = array();
    $entity_type_id = $this->fieldInfo->getSetting('target_type');
    $entity_definition = \Drupal::entityManager()->getDefinition($entity_type_id);

    // Determine target bundle restrictions.
    $target_bundle_key = NULL;
    if (!$target_bundles = $this->getTargetBundles()) {
      $target_bundle_key = $entity_definition->getKey('bundle');
    }

    foreach ($values as $value) {
      if(is_numeric($value)){
        $label_key = $entity_definition->getKey('id');
      }
      else{
        $label_key = $entity_definition->getKey('label');
      }
      $query = \Drupal::entityQuery($entity_type_id)->condition($label_key, $value);
      if ($target_bundles && $target_bundle_key) {
        $query->condition($target_bundle_key, $target_bundles, 'IN');
      }
      if ($entities = $query->execute()) {
        $return[] = array_shift($entities);
      }
      else {
        throw new \Exception(sprintf("No entity '%s' of type '%s' exists.", $value, $entity_type_id));
      }
    }
    return $return;
  }