[12.x] add toJson to Request

[braxey]

Make requests Jsonable to facilitate debugging.

Example: Want to easily see what's in a request at the beginning of a non-GET or XHR request:

public function controllerAction(Request $request)
{
   logger()->debug($request->toJson());
   ...
}

[henzeb]

You can do logger()->debug('my request', $request->toArray()) instead.

[devajmeireles]

You can do logger()->debug('my request', $request->toArray()) instead.

It makes sense, but there are dozens of other use cases for toJson beyond the log example.

[taylorotwell]

Thanks for your pull request to Laravel!

Unfortunately, I'm going to delay merging this code for now. To preserve our ability to adequately maintain the framework, we need to be very careful regarding the amount of code we include.

If applicable, please consider releasing your code as a package so that the community can still take advantage of your contributions!