Issue #2208633 by sun: Add a Yaml class to Drupal\Component\Serialization.

core/includes/common.inc

.../lib/Drupal/Component/Discovery/DiscoverableInterface.php

core/lib/Drupal/Component/Discovery/YamlDiscovery.php

...nent/Serialization/Exception/InvalidDataTypeException.php

...Drupal/Component/Serialization/SerializationInterface.php

core/lib/Drupal/Component/Serialization/Yaml.php

core/lib/Drupal/Core/Asset/LibraryDiscovery.php

core/lib/Drupal/Core/Config/ConfigManager.php

core/lib/Drupal/Core/Config/FileStorage.php

core/lib/Drupal/Core/DependencyInjection/YamlFileLoader.php

core/lib/Drupal/Core/Extension/InfoParser.php

core/lib/Drupal/Core/Extension/InfoParserException.php

core/lib/Drupal/Core/Extension/ModuleHandler.php

.../config/lib/Drupal/config/Controller/ConfigController.php

.../config/lib/Drupal/config/Form/ConfigSingleExportForm.php

.../config/lib/Drupal/config/Form/ConfigSingleImportForm.php

.../lib/Drupal/config/Tests/ConfigSingleImportExportTest.php

...lib/Drupal/config/Tests/Storage/ConfigStorageTestBase.php

...onfig/lib/Drupal/config/Tests/Storage/FileStorageTest.php

...odules/menu_link/lib/Drupal/menu_link/StaticMenuLinks.php