Copy internal SQLResultCasing from ORM

[franmomu]

Subject

When using the bundle along with symfony error handler the user gets a deprecation warning about using an internal trait:

The "Doctrine\ORM\Internal\SQLResultCasing" trait is considered internal. It may change without further notice. You should not use it from "SimpleThings\EntityAudit\AuditReader".

I've copied the trait to our domain.

I am targeting this branch, because these changes are BC.

Changelog

### Fixed
- Deprecation warning about using `SQLResultCasing` internal trait

[VincentLanglet]

phpcsfixer to fix