Use validation exception instead of building response in a Controller

[mpaden3]

Hi!

This PR changes the way validation response is built. Previous code relied upon a function in base Controller class that builds the validation response. That approach had a couple of problems:

• You have to inject ValidatorInterface to every POST/PATCH route.
• You have to check manually in every route if there are any validation errors. This forces you to repeat the same logic in every route in your application (4 lines of code).
• you are handling error case outside JsonApiErrorHandlerEvent class.

With this PR, validate() function is added to base controller that throws ValidationExeption. Then, the logic that builds JsonApi error response is moved to JsonApiErrorHandlerEvent and ValidationErrorDocument.

This removes some unnecessary repeating of logic in every specific Controller class and ValidatorInterface dependency. Also,
it moves the rest of the logic to the right place. Original validationErrorResponse() function is not removed, but marked as deprecated to keep the bundle backward compatible.

[AlexLisenkov]

What is this parameter used for?

[mpaden3]

This function overrides rather complicated base function from AbstractErrorDocument and it needs to have the same signature. Why does getter function have a parameter, you should ask the maintainers of woohoolabs\yin package :)
It is called by Responder class to determine error code of the request. In this case I can't see a use case where we need to change to a different error code for a validation error (it should always be 422). Still, I could always add code that returns that parameter if it is != null.