Fix config schema

Regarding the configuration structure:

It should be at each layout plugin using Layout Options to declare its own config schema, something like:

layout_plugin.settings.bootstrap_grid_row_2:
  type: layout_plugin.settings
  mapping:
    ...

It is not possible to try to generate it dynamically because of the core issue #3070463: Allow adding dynamic configuration schema:

I started something like:

// .module

use Drupal\layout_options\HookHandler\ConfigSchemaInfoAlter;

/**
 * Implements hook_config_schema_info_alter().
 */
function layout_options_config_schema_info_alter(array &$definitions): void {
  /** @var \Drupal\layout_options\HookHandler\ConfigSchemaInfoAlter $instance */
  $instance = \Drupal::service('class_resolver')
    ->getInstanceFromDefinition(ConfigSchemaInfoAlter::class);
  $instance->alter($definitions);
}

declare(strict_types = 1);

namespace Drupal\layout_options\HookHandler;

use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
use Drupal\Core\Layout\LayoutPluginManagerInterface;
use Drupal\layout_options\LayoutOptionPluginManager;
use Symfony\Component\DependencyInjection\ContainerInterface;

/**
 * Alter config schema.
 */
class ConfigSchemaInfoAlter implements ContainerInjectionInterface {

  /**
   * The layout plugin manager.
   *
   * @var \Drupal\Core\Layout\LayoutPluginManagerInterface
   */
  protected LayoutPluginManagerInterface $layoutPluginManager;

  /**
   * The layout options plugin manager.
   *
   * @var \Drupal\layout_options\LayoutOptionPluginManager
   */
  protected LayoutOptionPluginManager $layoutOptionPluginManager;

  /**
   * Constructor.
   *
   * @param \Drupal\Core\Layout\LayoutPluginManagerInterface $layoutPluginManager
   *   The layout plugin manager.
   * @param \Drupal\layout_options\LayoutOptionPluginManager $layoutOptionPluginManager
   *   The layout options plugin manager.
   */
  public function __construct(
    LayoutPluginManagerInterface $layoutPluginManager,
    LayoutOptionPluginManager $layoutOptionPluginManager
  ) {
    $this->layoutPluginManager = $layoutPluginManager;
    $this->layoutOptionPluginManager = $layoutOptionPluginManager;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container): self {
    return new self(
      $container->get('plugin.manager.core.layout'),
      $container->get('plugin.manager.layout_options')
    );
  }

  /**
   * Alter the config schema to provide layout settings schema dynamically.
   *
   * @param array $definitions
   *   Associative array of configuration type definitions keyed by schema type
   *   names. The elements are themselves array with information about the type.
   */
  public function alter(array &$definitions): void {
    $layoutDefinitions = $this->layoutPluginManager->getDefinitions();
    foreach ($layoutDefinitions as $layoutDefinition) {
      if ($layoutDefinition->getClass() != 'Drupal\layout_options\Plugin\Layout\LayoutOptions') {
        continue;
      }


      $definitions['layout_plugin.settings.' . $layoutDefinition->id()] = [
        'type' => 'layout_plugin.settings',
        'mapping' => [

        ],
      ];
    }
  }

}

Also the structure of the aved configuration depends its value, multi true or false, see screenshot:

So the dynamic declaration for one layout would require to instanciate the LayoutOptions plugin, parse the layout options declaration for this layout (which logic is in the LayoutOptions plugin and not in the LayoutOptionPluginManager), see the available options and generate the config schema accordingly.

Currently, I will try to provide some base schema type that will be usable by contrib or custom layouts.

And I need to check for layout_options_ui.

Also no need to provide config schema per layout options plugins because all of them save strings.