Support for cross bundle resource types

This adjustment fixed the crash:

    $entity_type = $this->entityTypeManager->getDefinition($resource_type->getEntityTypeId());
    $entity_type_label = $schema_type === 'collection' ? $entity_type->getPluralLabel() : $entity_type->getSingularLabel();
    if ($resource_type->getBundle() !== NULL && $bundle_type = $entity_type->getBundleEntityType()) {
      $bundle = $this->entityTypeManager->getStorage($bundle_type)->load($resource_type->getBundle());
      return $this->t(rtrim('@bundle_label @entity_type_label'), [
        '@bundle_label' => Unicode::ucfirst($bundle->label()),
        '@entity_type_label' => $entity_type_label,
      ]);
    }

    return $this->t(rtrim('@entity_type_label'), [
      '@entity_type_label' => Unicode::ucfirst($entity_type_label),
    ]);
  }

Here is a patch. I know the plan is to use an array of resource types for cross bundle over a union, but this way it won't crash and returns some data.