Add option to display the login button when user is not logged in

This was pretty easy to do. Here is the code if someone wants to make a patch. Just put this in the render function before the $element array. For a full solution, we'll also have to create a new field 'login_label' in the settings form to hold the 'Login to add your @bundle_label' chain int the way the 'Add a new entry' is done in defineOptions() and buildOptionsForm(). For those who can't wait for a patch, the same can be achieved in hook_preprocess_views_view: filter on $variables['display_id'] and work the $variables['header']['add_content_by_bundle'] array.

    // Start new code
    if (!$access) {
       $bundle_info = \Drupal::service("entity_type.bundle.info")->getBundleInfo($entity_type->id());
       $bundle_label = $bundle_info[$bundle_type]['label'];
       $this->options['label'] = $this->t('Login to add your @bundle_label', ['@bundle_label' => $bundle_label]);
       $url = Url::fromRoute('user.login', [], ['query' => $params]);
       $access = $this->accessManager->checkNamedRoute('user.login', [], $account);
    }
    // End of new code
    // Assemble elements into a link render array.
    $element = [
      '#type' => 'link',
      '#title' => $this->options['label'],
      '#url' => $url,
      '#options' => [
        'attributes' => ['class' => $classes],
      ],
      '#access' => $access,
    ];