Added DeprecatedServicePropertyTrait to simplify deprecating injected services/properties

The trait simplifies deprecating properties on classes.

Usage

Situation: the deprecated entity.manager service is replaced in a class, to avoid breaking subclasses that might still use it, the trait can be used:

• Remove the $entityManager property, add the replacements instead
• Change the constructor, in case of entity manager, the entity_type.manager is a backwards compatible replacement as the entity manager implements EntityTypeManager as well.
• Add the DeprecatedServicePropertyTrait
• Define the removed properties and their service ID in the $deprecatedProperties property

The result then looks like this:

class EntityConverter implements ParamConverterInterface {
  use DeprecatedServicePropertyTrait;

  /**
   * {@inheritdoc}
   */
  protected $deprecatedProperties = ['entityManager' => 'entity.manager'];

  /**
   * Entity type manager which performs the upcasting in the end.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  protected $entityTypeManager;

  /**
   * Entity repository.
   *
   * @var \Drupal\Core\Entity\EntityRepositoryInterface
   */
  protected $entityRepository;

  /**
   * The language manager.
   *
   * @var \Drupal\Core\Language\LanguageManagerInterface
   */
  protected $languageManager;

  /**
   * Constructs a new EntityConverter.
   *
   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
   *   The entity type manager.
   * @param \Drupal\Core\Language\LanguageManagerInterface|null $language_manager
   *   (optional) The language manager. Defaults to none.
   * @param \Drupal\Core\Entity\EntityRepositoryInterface $entity_repository
   *   The entity repository.
   */
  public function __construct(EntityTypeManagerInterface $entity_type_manager, LanguageManagerInterface $language_manager = NULL, EntityRepositoryInterface $entity_repository = NULL) {
    if ($entity_type_manager instanceof EntityManagerInterface) {
      @trigger_error('Passing the entity.manager service to EntityConverter::__construct() is deprecated in Drupal 8.7.0 and will be removed before Drupal 9.0.0. Pass the entity_type.manager service instead. See https://www.drupal.org/node/2549139.', E_USER_DEPRECATED);
    }
    $this->entityTypeManager = $entity_type_manager;
    if ($entity_repository) {
      $this->entityRepository = $entity_repository;
    }
    else {
      @trigger_error('The entity.repository service must be passed to EntityConverter::__construct(), it is required before Drupal 9.0.0. See https://www.drupal.org/node/2549139.', E_USER_DEPRECATED);
      $this->entityRepository = \Drupal::service('entity.repository');
    }
    $this->languageManager = $language_manager;
  }