JsonInputFormatter and JsonOutputFormatter consistancy

[JamesNK]

JsonInputFormatter
JsonOutputFormatter

• On JsonInputFormatter the CreateJsonReader and CreateJsonSerializer method are public and virtual.
• On JsonOutputFormatter the CreateJsonWriter and CreateJsonSerializer methods are private.

Should these methods be consistent between input and output formatters?

• JsonOutputFormatter implements IJsonOutputFormatter
• JsonInputFormatter doesn't implement an interface.

Is IJsonOutputFormatter required? It doesn't have any methods and is only used in one place.

[danroth27]

Let's deal with the IJsonOutputFormatter issue separately: #2715.

We should go ahead and make CreateJsonWriter and CreateJsonSerializer public.

[ajaybhargavb]

4a4b8ec