[HttpFoundation] fixed Request::getPreferredLanguage()

Previous PR #7378 was wrong and adding BC break. Resolution for short languages codes is now done in `Request::getPreferredLanguage()` method.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7378