Make the Request available to the Formatter\Rendering event (#1721)

This is important because extensions may wish to render post content
differently depending on Request factors such as the actor. For example,
an attachments extension might wish to hide attachments from guests.

This solution is a bit of a hack-job for now, but soon when we refactor
the API layer to use tobscure/json-api-server, and also refactor the
Formatter layer, it can be revised.

src/Api/Controller/AbstractSerializeController.php

@@ -102,7 +102,7 @@ abstract class AbstractSerializeController implements RequestHandlerInterface
         );
 
         $serializer = static::$container->make($this->serializer);
-        $serializer->setActor($request->getAttribute('actor'));
+        $serializer->setRequest($request);
 
         $element = $this->createElement($data, $serializer)
             ->with($this->extractInclude($request))