fn module_constants(vm: &mut VM, _: Value, args: &Args2) -> VMResult {
    args.check_args_num(0)?;
    let v = vm
        .enumerate_const()
        .into_iter()
        .map(|id| Value::symbol(id))
        .collect();
    Ok(Value::array_from(v))
}
## singleton method Module.constants
- constants -> [[Symbol]]

https://docs.ruby-lang.org/ja/latest/method/Module/s/constants.html
ruruby/src/builtin/module.rs