TermName.php

<?php

namespace Drupal\taxonomy\Plugin\views\field;

use Drupal\Core\Form\FormStateInterface;
use Drupal\views\Plugin\views\field\EntityField;
use Drupal\views\ResultRow;

/**
 * Displays taxonomy term names and allows converting spaces to hyphens.
 *
 * @ingroup views_field_handlers
 *
 * @ViewsField("term_name")
 */
class TermName extends EntityField {
    
    /**
     * {@inheritdoc}
     */
    public function getItems(ResultRow $values) {
        $items = parent::getItems($values);
        if ($this->options['convert_spaces']) {
            foreach ($items as &$item) {
                // Replace spaces with hyphens.
                $name = $item['raw']->get('value')
                    ->getValue();
                // @todo Add link support https://www.drupal.org/node/2567745
                $item['rendered']['#context']['value'] = str_replace(' ', '-', $name);
            }
        }
        return $items;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['convert_spaces'] = [
            'default' => FALSE,
        ];
        return $options;
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        $form['convert_spaces'] = [
            '#title' => $this->t('Convert spaces in term names to hyphens'),
            '#type' => 'checkbox',
            '#default_value' => !empty($this->options['convert_spaces']),
        ];
        parent::buildOptionsForm($form, $form_state);
    }

}