Issue #1880424 by linclark, effulgentsia: Handle entity references on import.

core/modules/hal/hal.services.yml

...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/NormalizerBase.php

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

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

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

core/modules/rest/rest.services.yml

...upal/serialization/EntityResolver/ChainEntityResolver.php

.../serialization/EntityResolver/EntityResolverInterface.php

...l/serialization/EntityResolver/UuidReferenceInterface.php

.../lib/Drupal/serialization/EntityResolver/UuidResolver.php

...pal/serialization/RegisterEntityResolversCompilerPass.php

...lization/lib/Drupal/serialization/SerializationBundle.php

...ion/lib/Drupal/serialization/Tests/EntityResolverTest.php

...ib/Drupal/serialization/Tests/EntitySerializationTest.php

...ion/lib/Drupal/serialization/Tests/NormalizerTestBase.php

core/modules/serialization/serialization.services.yml