Add json.unparse: RTTI-less conversion from json.Value to []u8

[bullyingteen]

This is a follow up PR to the smalltalk we had in Discord/General/Beginners.

Introduction

While trying out odin's encoding/json module I've found out that the only way to convert json.Value to []u8/string was to use json.marshal (docs lack that information).
Which feels very unnatural and misleading to me as a C/C++ developer. So I did implement json.unparse. It probably has a tiny bit of performance boost due to it being RTTI-less.

Added test case for json.unparse, tested it on my windows 11.

Named it json.unparse for consistency with json.parse, but naming suggestions are wellcome.

Bonus

Fixed an Unsupported_Type error in json.marshal on (rawptr)nil values.

P.S.

json.marshal uses Raw_Map routines when converting json.Object, but it requires runtime.Type_Info for accessing Map_Info hence I used simple k/v for-loop over map. Let me know if traversing Raw_Map buckets is preferred for some reason. I might implement it that way instead.