Issue #1924220 by linclark: Support serialization in hal+json.

core/MAINTAINERS.txt

core/modules/hal/hal.info.yml

core/modules/hal/hal.module

core/modules/hal/lib/Drupal/hal/Encoder/JsonEncoder.php

core/modules/hal/lib/Drupal/hal/HalBundle.php

core/modules/hal/lib/Drupal/hal/HalSubscriber.php

...odules/hal/lib/Drupal/hal/Normalizer/EntityNormalizer.php

...b/Drupal/hal/Normalizer/EntityReferenceItemNormalizer.php

...les/hal/lib/Drupal/hal/Normalizer/FieldItemNormalizer.php

...modules/hal/lib/Drupal/hal/Normalizer/FieldNormalizer.php

.../modules/hal/lib/Drupal/hal/Normalizer/NormalizerBase.php

core/modules/hal/lib/Drupal/hal/Tests/NormalizeTest.php

core/modules/hal/lib/Drupal/hal/Tests/NormalizerTestBase.php

.../modules/rest/lib/Drupal/rest/LinkManager/LinkManager.php

...rest/lib/Drupal/rest/LinkManager/LinkManagerInterface.php

.../rest/lib/Drupal/rest/LinkManager/RelationLinkManager.php

.../Drupal/rest/LinkManager/RelationLinkManagerInterface.php

...ules/rest/lib/Drupal/rest/LinkManager/TypeLinkManager.php

.../lib/Drupal/rest/LinkManager/TypeLinkManagerInterface.php

core/modules/rest/lib/Drupal/rest/RestBundle.php