[5.6] ResourceResponse returns the resource data instead of JSON on Original

[olivernybroe]

By setting original to the model on resources, we can in our tests check directly if the model is the correct one, by just getting the original attribute on the response.
Often I don't want to check if the JSON is formatted correctly, just interested if the model is the correct one.

Pull request send to master instead of 5.5, as commented in #22429

[olivernybroe]

The reason for setting the original before withResponse is run, is for the ability to still change original in your withResponse function.
So withResponse is always the last thing that touches the response object.