add filed name

[qicosmos]

add field_name:

struct sub {
  int id;
};

struct person {
  ns::ns2::Color color;
  int id;
  sub s;
  std::string str;
};

TEST_CASE("test field string") {
  constexpr auto field_name1 = iguana::field_string<&person::color>();
  constexpr auto field_name2 = iguana::field_string<&person::id>();
  constexpr auto field_name3 = iguana::field_string<&person::s>();
  constexpr auto field_name4 = iguana::field_string<&person::str>();
  CHECK(field_name1 == "color");
  CHECK(field_name2 == "id");
  CHECK(field_name3 == "s");
  CHECK(field_name4 == "str");
}

rename enum_reflection to field_reflection