[FEATURE] Make sure all cacheability metadata is added

This is the first I found. This still needs all the work to be done, I just wanted to have this somewhere.

We're doing the same REST core does, the problem comes with the includes. Since core is not supporting that feature we're on our own.

I believe I know what needs to happen, but I want to get familiar with the render cache internals first.

1. +++ b/src/Normalizer/EntityNormalizer.php
   @@ -178,13 +180,20 @@ class EntityNormalizer extends NormalizerBase implements DenormalizerInterface,
   +      return (new NullFieldNormalizerValue())->addCacheableDependency($access);
   

   You're gonna make me want to write an article about the Null object pattern! Article bait.

   :+1:

2. +++ b/src/Normalizer/Value/NullFieldNormalizerValue.php
   @@ -0,0 +1,36 @@
   +    return NULL;
   

   <?php
   return $this->cardinality == 1 ?
   NULL :
   [];

I've given a try to the issue. There is probably a better way to do this but I didn't know how to bubble the cacheability metadata. The url generator is bubbling up some metadata for the render context, but I'm not sure how to do that in a clean way.

This approach makes all the Normalizer Value classes aware of the cacheability metadata. Then the recursivity in the serializer surfaces that to the DocumentRootNormalizer. The DocumentRootNormalizer now gets the $response object's cacheability metadata and alters it to add the gathered dependencies.

Maybe Wim can look at the patch and give some recommendations without having to get a lot of context in the jsonapi code.

I'm sorry testbot, this should make you happy.

Old tests are green. We need new tests before we merge this.

This is now ready for code review, @dawehner.

I'm going to self-merge this because it's blocking #2766147: [BUGFIX] Apply error format during serialization.

@dawehner please review it anyways and I'll create a follow up to address any concern you may have.

Feature video https://youtu.be/-r60edg1Tfg. In case anyone is interested.