\Drupal\Component\Serialization\Yaml::decodeTags() added to convert TaggedValue objects into more useful value

\Drupal\Component\Serialization\Yaml::decodeTags() has been added to allow \Symfony\Component\Yaml\Tag\TaggedValue objects to be converted into more useful objects. This underpins the new !translate YAML tag - see Recipe's recipe.yml can be translated.

To use this method you must parse Yaml using the \Symfony\Component\Yaml\Yaml::PARSE_CUSTOM_TAGS flag which is the case for \Drupal\Component\Serialization\Yaml::decode().

For example to parse a recipe file and convert all the !translate tagged values to \Drupal\Core\StringTranslation\TranslatableMarkupobjects

use Drupal\Component\Serialization\Yaml;
use Drupal\Core\StringTranslation\TranslatableMarkup;

$recipe_data = Yaml::decode(file_get_contents('PATH_TO/recipe.yml'));
$recipe_data = Yaml::decodeTags($recipe_data, ['translate' => TranslatableMarkup::class]);