Issue #1931976 by linclark, effulgentsia: Support deserialization for hal+json.

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

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

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

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