[HttpKernel] Fixed Inconsistent locale handling in subrequests

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #6932 
| License       | MIT
| Doc PR        | -

The fix consists in passing the locale in the controller reference,
inside the routablefragment renderer.