Helper callback for uasort() to sort configuration entities by weight and label.
public static function sort($a, $b) {
  $a_weight = isset($a->weight) ? $a->weight : 0;
  $b_weight = isset($b->weight) ? $b->weight : 0;
  if ($a_weight == $b_weight) {
    $a_label = $a
      ->label();
    $b_label = $b
      ->label();
    return strnatcasecmp($a_label, $b_label);
  }
  return $a_weight < $b_weight ? -1 : 1;
}