getFieldLabelOptions example

$field_row = parent::buildFieldRow($field_definition, $form, $form_state);

    $field_name = $field_definition->getName();
    $display_options = $this->entity->getComponent($field_name);

    // Insert the label column.     $label = [
      'label' => [
        '#type' => 'select',
        '#title' => $this->t('Label display for @title', ['@title' => $field_definition->getLabel()]),
        '#title_display' => 'invisible',
        '#options' => $this->getFieldLabelOptions(),
        '#default_value' => $display_options ? $display_options['label'] : 'above',
      ],
    ];

    $label_position = array_search('plugin', array_keys($field_row));
    $field_row = array_slice($field_row, 0, $label_position, TRUE) + $label + array_slice($field_row, $label_position, count($field_row) - 1, TRUE);

    // Update the (invisible) title of the 'plugin' column.     $field_row['plugin']['#title'] = $this->t('Formatter for @title', ['@title' => $field_definition->getLabel()]);
    if (!empty($field_row['plugin']['settings_edit_form']) && ($plugin = $this->entity->getRenderer($field_name))) {
      $plugin_type_info = $plugin->getPluginDefinition();