Allow to define Map type while decoding

[Mahad-10]

trafficstars

MsgPack serializer currently can't specify the types of keys and values for a Map during decoding. It would be beneficial to introduce a feature like:

Deserializer deserializer = Deserializer(
    list,
    extDecoder: extDecoder,
    copyBinaryData: copyBinaryData,
    mapType: mapType,
  );

For reference, something like: https://github.com/ugorji/go/blob/07c54c229a5acac2d5bc739820a3ecc5411b7b33/codec/decode.go#L216