Support deserializing to Map<String, Object>

[jerolba]

Support deserializing group elements to a Map<String, Object>

message foo{
  required int64 id;
  required binary name (STRING);
  required group bar {
      required int32 code;
      required double value;
      required int64 attr;
  }
}

Can be deserialized to

record Foo(long id, String name, Map<String, Object> bar) {}

and bar Map will have as keys code, value and attr .

The process can be applied recursively and even to the root object, deserializing to a Map where keys are id, name and bar