code: public static Slice codePointToUtf8(int codePoint)
      {
          Slice utf8 = Slices.allocate(lengthOfCodePoint(codePoint));
          setCodePointAt(codePoint, utf8, 0);
          return utf8;
      }
docs: Convert the code point to UTF-8.
  <p>
  
  @throws InvalidCodePointException if code point is not within a valid range