Issue #3323741 by andypost, Spokje, catch, longwave: upgrade Symfony dependencies to RC1

composer.json

composer.lock

composer/Composer.php

composer/Generator/ComponentGenerator.php

composer/Metapackage/CoreRecommended/composer.json

composer/Metapackage/DevDependencies/composer.json

composer/Metapackage/PinnedDevDependencies/composer.json

core/composer.json

core/lib/Drupal/Component/DependencyInjection/composer.json

core/lib/Drupal/Component/EventDispatcher/composer.json

core/lib/Drupal/Component/HttpFoundation/composer.json

core/lib/Drupal/Component/Plugin/composer.json

core/lib/Drupal/Component/Serialization/composer.json

...dTests/Composer/Template/ComposerProjectTemplatesTest.php