fn regexp_escape(vm: &mut VM, _: Value, args: &Args2) -> VMResult {
    args.check_args_num(1)?;
    let mut arg0 = vm[0];
    let string = arg0.expect_string("1st arg")?;
    let regexp = Value::string(regex::escape(string));
    Ok(regexp)
}
Regexp.escape(string) -> String
Regexp.quote(string) -> String
https://docs.ruby-lang.org/ja/latest/method/Regexp/s/escape.html
ruruby/src/builtin/regexp.rs