Add an auto_alias compiler pass

Discussion see https://github.com/symfony/symfony/issues/11460

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | [#11460]
| License       | MIT
| Doc PR        |
We only use camelCase variables in Symfony. Can you make the change everywhere? Thanks.