[Routing] Moving include instruction to separate method

| Q             | A
| ------------- | ---
| Bug fix?      | [yes]
| New feature?  | [no]
| BC breaks?    | [no]
| Deprecations? | [no]
| Tests pass?   | [yes]
| Fixed tickets | #12106
| License       | MIT
It's better to align the docblock like this:

```php
@param string        $file   File to include
@param PhpFileLoader $loader the loader variable is exposed to the included file below
```