[REQ] Lossless JSON parsing for JavaScript generated libraries.

Is your feature request related to a problem? Please describe.

When creating an API client using the JavaScript generator, when parsing JSON data with large integers and converting data types, such as:

{ "id" : "21473794133340466" }

The data tends to get misrepresented (that particular number turns into 21473794133340464), as JavaScript is bad at handling large integers, this happens when the parsed body is returned using superagent. This is a pretty well known problem and many JSON parsing libraries exist that implement special classes for this case.

Describe the solution you'd like

It would be great if the default request body parsing would implement something like this or at least allow for a flag to be added to the generator that would enable such a feature.

Describe alternatives you've considered

Additional context

Start at the JavaScript generator's default superagent response-body parsing and review the requested lossless-json approach or generator flag. Use the large-integer example from the issue to verify that parsing preserves the original value, and ensure the selected behavior is covered by an appropriate generator test.