[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
given that it is static, please use ``self::`` instead of ``$this->``