Issue #1894508 by linclark, damiankloip: Update symfony/serializer.

core/composer.lock

core/lib/Drupal/Core/Serialization/ComplexDataNormalizer.php

core/lib/Drupal/Core/Serialization/ListNormalizer.php

core/lib/Drupal/Core/Serialization/TypedDataNormalizer.php

core/lib/Drupal/Core/Serialization/XmlEncoder.php

...dules/jsonld/lib/Drupal/jsonld/JsonldEntityNormalizer.php

...nld/lib/Drupal/jsonld/JsonldEntityReferenceNormalizer.php

...es/jsonld/lib/Drupal/jsonld/JsonldFieldItemNormalizer.php

...es/jsonld/lib/Drupal/jsonld/JsonldRdfSchemaNormalizer.php

...ib/Drupal/serialization_test/SerializationTestEncoder.php

...Drupal/serialization_test/SerializationTestNormalizer.php

core/vendor/autoload.php

core/vendor/composer/autoload_real.php

core/vendor/composer/installed.json

...ny/serializer/Symfony/Component/Serializer/.gitattributes

...fony/serializer/Symfony/Component/Serializer/CHANGELOG.md

...zer/Symfony/Component/Serializer/Encoder/ChainDecoder.php

...zer/Symfony/Component/Serializer/Encoder/ChainEncoder.php

...Symfony/Component/Serializer/Encoder/DecoderInterface.php

...Symfony/Component/Serializer/Encoder/EncoderInterface.php