Plugin types should use PHP attributes instead of annotations

Related change record: https://www.drupal.org/node/3395575 for plugins

Convert a plugin type

• Introduce Attribute object
• Provide a 1to1 mapping between the annotation keys and attribute parameter names
• Update constructor of plugin manager and pass along the new attribute class, followed by the Annotation class for backwards compatibility
• DefaultPluginManager::__construct() supports 3 cases
  • Only an Annnotation class (deprecated, uses AnnotatedClassDiscovery)
  • An Attribute class, followed by an Annotation class (recommended for existing plugin types to avoid BC breaks. Uses AttributeDiscoveryWithAnnotations, Drupal 11 will ignore the Annotation class parameter then)
  • An Attribute class (recommended for new plugin types, uses AttributeClassDiscovery
• The code examples below use full namespaces for clarity, implementations may use use statements and just Action::class for example.

Before

// Annotation class
class Action extends \Drupal\Component\Annotation\Plugin {
...
}

// Plugin manager:
public function __construct(\Traversable $namespaces, CacheBackendInterface $cache_backend, ModuleHandlerInterface $module_handler) {
  parent::__construct('Plugin/Action', $namespaces, $module_handler, 'Drupal\Core\Action\ActionInterface', 'Drupal\Core\Annotation\Action');
}

After

// Attribute class
#[\Attribute(\Attribute::TARGET_CLASS)]
class Action extends \Drupal\Component\Plugin\Attribute\Plugin {
…
}

// Plugin manager
 public function __construct(\Traversable $namespaces, CacheBackendInterface $cache_backend, ModuleHandlerInterface $module_handler) {
   parent::__construct('Plugin/Action', $namespaces, $module_handler, 'Drupal\Core\Action\ActionInterface', 'Drupal\Core\Action\Attribute\Action', 'Drupal\Core\Annotation\Action');
}

Not providing an attribute class is deprecated in Drupal 11.2 and will no longer be supported in Drupal 12.