When fetching related resources, getResourceType() in CurrentContext gets the wrong resource type.

When fetching related resources, getResourceType() in CurrentContext gets the resource type fixed to the route instead of retrieving it from the related resource.

This results in the "Invalid nested filtering. Invalid entity reference" error from resolveInternal() in the FieldResolver because the included fields are checked against the wrong entity type.

Example:

We have a node of bundle 'article' with a paragraph field 'field_paragraphs'.

The paragraph has a media reference field 'field_media_image'.

We want to get a list of paragraphs with the field_media_image included:

http://url/jsonapi/node/article/UUID/field_paragraphs?include=field_media_image,field_media_image.field_image

The jsonapi module checks if field_media_image is a field of entity type 'node' instead of 'paragraph'.

See Routes.php line 143 for the route we're using:

      // Related resource, like /jsonapi/file/photo/123/comments.
      $route_related = (new Route(sprintf('%s/{%s}/{related}', $route_base_path, $resource_type->getEntityTypeId()), $defaults))
        ->setRequirement('_entity_type', $resource_type->getEntityTypeId())
        ->setRequirement('_bundle', $resource_type->getBundle())
        ->setRequirement('_permission', 'access content')
        ->setRequirement('_jsonapi_custom_query_parameter_names', 'TRUE')
        ->setOption('parameters', $parameters)
        ->setOption('_auth', $this->authProviderList())
        ->setMethods(['GET']);
      $route_related->addOptions($options);
      $collection->add($build_route_name('related'), $route_related);

In this example, CurrentContext is using file for the entity id instead of comments.