Pass the model to the security context when checking credentials.

Hello,

With this small change, the ProcessHandler pass the model to the isGranted method of the security context. This would allow either to use Symfony ACL system or to implement model-based authorization checks in a custom Voter. I have to do this in one of my project and I would prefer have this solution than simulating it with a custom pre-validation listener.

Regards,
Adirelle.

Adding a `getWorkflowObject()` method to `ModelInterface` is not a big change. And no it would not require to only use ACL, even if you pass the final object to `isGranted()` you can create some custom voters, all is about the class and attributes your voter will support.