Use regular upstream HttpKernel instead of Drupal's custom

Updated: Comment #N

Problem/Motivation

Drupal still uses a copy of the HttpKernel class which once was part of the Symfony Framework Bundle. However this class is long gone (deprecated in 2.2 and removed in 2.3) and therefore we also should get rid of our copy.

There are two candidates we could go for as a replacement for the custom http kernel:

1. Symfony\Component\HttpKernel\HttpKernel
2. Symfony\Component\HttpKernel\DependencyInjection\ContainerAwareHttpKernel

In fact the latter is the successor of the HttpKernel we copied over from the framework bundle and only differs from the former that it still manages the request scope.

Regrettably just swapping out our custom kernel with ContainerAwareHttpKernel causes problems all over the place. Unlike our implementation it sets the request to NULL before leaving the request scope. In order to make our services compatible with the ContainerAwareHttpKernel we'd need to adapt them such they accept NULL for the $request parameter.

The other alternative (switching to Symfony\Component\HttpKernel\HttpKernel) requires us to convert all our services to the recently introduced request_stack. Given that Symfony moves away from request service as well as from container scopes, and that we have to touch all our request-dependent services anyway, this seems the better alternative.

Proposed resolution

1. Convert all request-dependent services to request_stack
2. Get rid of the request-scope.
3. Remove Drupal\Core\HttpKernel and replace it with Symfony\Component\HttpKernel\HttpKernel

Remaining tasks

User interface changes

API changes