[8.x] Add raw() method to factory

[dwightwatson]

This re-introduces the raw() method which was previously available on model factories.

I personally find this useful for when testing requests and I want to pass through valid model data, I can just get the raw attributes in an array and pass them straight into the request.

It looks like I'm not the only one who misses raw():

• Cannot extend model factories #34166
• https://laracasts.com/discuss/channels/testing/what-is-the-laravel-8-replacement-for-factory-raw

Thanks 🙂