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

src/common/json.h

@@ -0,0 +1,50 @@
+#pragma once
+
+#include <winrt/Windows.Foundation.h>
+#include <winrt/Windows.Data.Json.h>
+
+#include <optional>
+
+namespace json
+{
+  using namespace winrt::Windows::Data::Json;
+
+  std::optional<JsonObject> from_file(std::wstring_view file_name);
+
+  void to_file(std::wstring_view file_name, const JsonObject& obj);
+
+  inline bool has(
+    const json::JsonObject & o,
+    std::wstring_view name,
+    const json::JsonValueType type = JsonValueType::Object)
+  {
+    return o.HasKey(name) && o.GetNamedValue(name).ValueType() == type;
+  }
+
+  template<typename T>
+  inline std::enable_if_t<std::is_arithmetic_v<T>, JsonValue> value(const T arithmetic)
+  {
+    return json::JsonValue::CreateNumberValue(arithmetic);
+  }
+
+  template<typename T>
+  inline std::enable_if_t<!std::is_arithmetic_v<T>, JsonValue> value(T s)
+  {
+    return json::JsonValue::CreateStringValue(s);
+  }
+
+  inline JsonValue value(const bool boolean)
+  {
+    return json::JsonValue::CreateBooleanValue(boolean);
+  }
+
+  inline JsonValue value(JsonObject value)
+  {
+    return value.as<JsonValue>();
+  }
+
+  inline JsonValue value(JsonValue value)
+  {
+    return value; // identity function overload for convenience
+  }
+}