Remove RequestHandler class and service and add EntityResource methods to each route definition

The 2987610-9.patch patch was incorrect. I solved it by applying 2987610-9.patch and then reverting interdiff-removed-from-patch.txt.

Intended patch attached.

Fix for #9's failure.

1. +++ b/jsonapi.services.yml
   @@ -146,13 +146,8 @@ services:
      # Controllers.
   -  jsonapi.request_handler:
   -    class: \Drupal\jsonapi\Controller\RequestHandler
   -    arguments:
   -      - '@jsonapi.entity_resource'
      jsonapi.entity_resource:
        class: \Drupal\jsonapi\Controller\EntityResource
   -    public: false
   

   🚀😍

2. +++ b/src/Controller/EntityResource.php
   @@ -408,15 +408,15 @@ class EntityResource {
   -   * @param string $related_field
   +   * @param string $related
   

   This is to allow Drupal's routing system to handle this for us, right?

   Question: why change these signatures if we could also just update this in Routes:
   $relationship_route->addDefaults(['related' => $relationship_field_name]);
   to
   $relationship_route->addDefaults(['related_field' => $relationship_field_name]);

   That'd make this patch much smaller.

3. +++ b/src/Controller/EntityResource.php
   @@ -688,13 +688,13 @@ class EntityResource {
   diff --git a/src/Controller/RequestHandler.php b/src/Controller/RequestHandler.php
   
   diff --git a/src/Controller/RequestHandler.php b/src/Controller/RequestHandler.php
   deleted file mode 100644
   

   👏

4. +++ b/src/Routing/Routes.php
   @@ -29,7 +29,7 @@ class Routes implements ContainerInjectionInterface {
   -  const FRONT_CONTROLLER = 'jsonapi.request_handler:handle';
   +  const FRONT_CONTROLLER = 'jsonapi.entity_resource';
   

   It's no longer a front controller. It's just a controller. (Albeit the only one, at least for now.)

   I'd either rename this to CONTROLLER, or … get rid of it altogether, and just write

   RouteObjectInterface::CONTROLLER_NAME =>
    'jsonapi.entity_resource:getCollection'

   , for example.

5. +++ b/src/Routing/Routes.php
   @@ -232,16 +236,24 @@ class Routes implements ContainerInjectionInterface {
   +        'GET' =>    'getRelationship',
   +        'POST' =>   'createRelationship',
   +        'PATCH' =>  'patchRelationship',
   +        'DELETE' => 'deleteRelationship',
   

   Übernit: I <3 this whitespace, but Drupal core does not allow it.

6. +++ b/src/Routing/Routes.php
   @@ -232,16 +236,24 @@ class Routes implements ContainerInjectionInterface {
   +      foreach ($relationship_route_methods as $method) {
   +        $method_specific_relationship_route = clone $relationship_route;
   +        $method_specific_relationship_route->addDefaults([RouteObjectInterface::CONTROLLER_NAME => static::FRONT_CONTROLLER . ":{$relationship_controller_methods[$method]}"]);
   +        $method_specific_relationship_route->setMethods($method);
   +        $routes->add(static::getRouteName($resource_type, sprintf("%s.relationship.%s", $relationship_field_name, strtolower($method))), $method_specific_relationship_route);
   +      }
   

   🤘

7. +++ b/tests/src/Unit/Routing/RoutesTest.php
   @@ -71,11 +71,11 @@ class RoutesTest extends UnitTestCase {
   +    // - 12 routes; 3 fields * 4 HTTP methods.
   

   Nit: s/12 routes/12 relationship routes/

#16.2: Ahh, that makes sense. Too bad 😞

No further remarks. RTBC when the blocker lands!

For now, marking postponed.

Rebased #27 on top of not only #2987608: Move deserialization from RequestHandler to JsonApiParamEnhancer but also #2958554: Allow creation of file entities from binary data via JSON API requests, because #2958554 changes some things in EntityResource that conflict with some of the changes here. This is just for testing purposes in #2958554.

#2987608: Move deserialization from RequestHandler to JsonApiParamEnhancer just landed!

Needs work because of #27's failures.

👌

P.S.: I love the smell of a lovely diffstat in the morning: 11 files changed, 97 insertions(+), 184 deletions(-) 😍

d.o is again suffering from a race condition; in some places this is marked as Fixed, in others it's marked as RTBC. Let's fix that changing the status twice.