function amf0decTypedObj(buf) {
  let className = amf0decString(buf);
  let obj = amf0decObject(buf.slice(className.len - 1));
  obj.value.__className__ = className.value;
  return { len: className.len + obj.len - 1, value: obj.value };
}
AMF0 Decode Typed Object
@param {Buffer} buf
@returns {{len: number, value: ({}|*)}}