Issue #1935538 by linclark, effulgentsia: Switch REST to default to HAL.

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

core/modules/rest/lib/Drupal/rest/Tests/CreateTest.php

core/modules/rest/lib/Drupal/rest/Tests/DBLogTest.php

core/modules/rest/lib/Drupal/rest/Tests/DeleteTest.php

core/modules/rest/lib/Drupal/rest/Tests/RESTTestBase.php

core/modules/rest/lib/Drupal/rest/Tests/ReadTest.php

core/modules/rest/lib/Drupal/rest/Tests/UpdateTest.php

.../rest/lib/Drupal/rest/Tests/Views/StyleSerializerTest.php

core/modules/rest/rest.info.yml

core/modules/rest/rest.module