Use WinRT JSON parser instead of custom cpprestsdk solution (#822)

src/common/json.cpp

@@ -0,0 +1,26 @@
+#include "pch.h"
+#include "json.h"
+
+#include <fstream>
+
+namespace json
+{
+  std::optional<JsonObject> from_file(std::wstring_view file_name)
+  {
+    try
+    {
+      std::wifstream file(file_name.data(), std::ios::binary);
+      using isbi = std::istreambuf_iterator<wchar_t>;
+      return JsonValue::Parse(std::wstring{isbi{file}, isbi{}}).GetObjectW();
+    }
+    catch(...)
+    {
+      return std::nullopt;
+    }
+  }
+
+  void to_file(std::wstring_view file_name, const JsonObject & obj)
+  {
+    std::wofstream{file_name.data(), std::ios::binary} << obj.Stringify().c_str();
+  }
+}