Issue #3243437 by wells: Add 4-to-5 settings migration handling

<?php

namespace Drupal\ckeditor_codemirror\Plugin\CKEditor4To5Upgrade;

use Drupal\ckeditor5\HTMLRestrictions;

use Drupal\ckeditor5\Plugin\CKEditor4To5UpgradePluginInterface;

use Drupal\Core\Plugin\PluginBase;

use Drupal\filter\FilterFormatInterface;

/**

 * Provides the CKEditor 4 to 5 upgrade for CKEditor CodeMirror.

 *

 * @CKEditor4To5Upgrade(

 *   id = "codemirror",

 *   cke4_buttons = {},

 *   cke4_plugin_settings = {"codemirror"},

 *   cke5_plugin_elements_subset_configuration = {}

 * )

 */

class CodeMirror extends PluginBase implements CKEditor4To5UpgradePluginInterface {

  /**

   * {@inheritdoc}

   */

  public function mapCKEditor4ToolbarButtonToCKEditor5ToolbarItem(string $cke4_button, HTMLRestrictions $text_format_html_restrictions): ?array {

    throw new \OutOfBoundsException();

  }

  /**

   * {@inheritdoc}

   */

  public function mapCKEditor4SettingsToCKEditor5Configuration(string $cke4_plugin_id, array $cke4_plugin_settings): ?array {

    switch ($cke4_plugin_id) {

      case 'codemirror':

        // Exclude settings no longer supported in CKE5 plugin.

        $settings = [

          'enable' => $cke4_plugin_settings['enable'],

          'mode' => $cke4_plugin_settings['mode'],

          'options' => [

            'autoCloseBrackets' => $cke4_plugin_settings['options']['autoCloseBrackets'],

            'autoCloseTags' => $cke4_plugin_settings['options']['autoCloseTags'],

            'folding' => $cke4_plugin_settings['options']['enableCodeFolding'],

            'lineNumbers' => $cke4_plugin_settings['options']['lineNumbers'],

            'lineWrapping' => $cke4_plugin_settings['options']['lineWrapping'],

            'matchBrackets' => $cke4_plugin_settings['options']['matchBrackets'],

          ]

        ];

        return ['ckeditor_codemirror_source_editing' => $settings];

      default:

        throw new \OutOfBoundsException();

    }

  }

  /**

   * {@inheritdoc}

   */

  public function computeCKEditor5PluginSubsetConfiguration(string $cke5_plugin_id, FilterFormatInterface $text_format): ?array {

    throw new \OutOfBoundsException();

  }

}