Added a generic class resolver in addition to controller resolver

The controller resolver class from Symfony allows you to inject parameters into a callable (a method on a class for example)
as well as construct instances of controller classes.

The later functionality got copied out:

$instance = \Drupal::service('class_resolver')->getInstanceFromClassName('Drupal\foo\Bar\Baz');

If this class implements ContainerInjectionInterface the create() method is called.