Allow invokable services as controllers

Currently Drupal supports to set a fully qualified class name as a controller which implements the __invoke method however this is very limited since the controller is instantiated from it's string without having the option to pass services to the construct. This means that the invokable controller can't use any external services using dependency injection. I looked into how this is supported in Symfony Framework and it was easy to add this functionality to Drupal. As mentioned in the Symfony Framework documentation this is popular with the Action-Domain-Response (ADR) pattern.

Will work like this:

services.yml

services:
  controller.invoke:
    class: Drupal\invoke\Controller\InvokeController
    public: true

routing.yml

acme_invoke:
  path: /invoke
  defaults:
    _controller: controller.invoke
  requirements:
    _access: 'TRUE'

Of course in Drupal 8.5 (and higher) it will also work like this:

services.yml

services:
  Drupal\invoke\Controller\InvokeController
    public: true

routing.yml

acme_invoke:
  path: /invoke
  defaults:
    _controller: Drupal\invoke\Controller\InvokeController
  requirements:
    _access: 'TRUE'

The controller can in both cases be:
- A service with __invoke method registered in the container without having any arguments in the __construct
- A service with __invoke method not registered in the container with or without having any arguments in the __construct