YamlFileLoader loads YAML files service definitions.
Drupal does not use Symfony's Config component, and Symfony's dependency on it cannot be removed easily. Therefore, this is a partial but mostly literal copy of upstream, which does not depend on the Config component.
NOTE: 98% of this code is a literal copy of Symfony's YamlFileLoader.
This file does NOT follow Drupal coding standards, so as to simplify future synchronizations.
Hierarchy
class \Drupal\Core\DependencyInjection\YamlFileLoader