Allow @Factory annotation directly on input type classes #285

I could have sworn there was a discussion on this topic some time back. I looked around and couldn't find the ticket or a pull request, but maybe I'm overlooking it. If anyone can link that other ticket that'd be great.

But basically, this ticket is to discuss the fact that factory methods are often times nothing but boilerplate. In fact, I've only had to modify input fields a handful of times to date. These methods mostly consist of taking in params and passing them directly to properties of the input type. In fact, in our case, they already have the same names as well. I'd assume this is similar for most.

What this proposes is making the @Factory annotation optionally defined on the input type class, itself. I don't even see any need for args to handle anything here, just a direct mapping, when the annotation is defined on the input type class.

As for how the properties are populated, it's probably best that, like the factory method today, all of the properties assignments are passed to the input type class' constructor. This would also allow for some light field modification if someone deemed that necessary. For example taking a date string and instantiating a Date object to assign to the class' property.

Assuming the above with the constructor, the question then becomes, do you put the @Factory annotation on the constructor or the class?

The other thing that I'll add to this, because I know it'd be an issue for us, is validation. We do also add a simple validation call within our input type factories. Assuming this gets implement, I think there should also be a way to register an InputTypeValidatorInterface with the schema, that would then be called when an input type is constructed, passing that newly constructed input type object.