Issue #3226944: REST's Request handler doesn't resolve $data argument for put method
Changed condition so, that argument are properly resolved for put and delete methods of REST resource plugins. Refactoring tests in \Drupal\Tests\rest\Kernel\RequestHandlerTest to avoid code duplication and to allow test basic behavior of \Drupal\rest\RequestHandler::handle and $data argument resolution separately.
Edited by Sergei Brill