function toConjoiningJamo(string) {
  if (!hasCompatibilityOrSyllable(string)) {
    return string;
  }

  const result = [];
  for (let i = 0; i < string.length; i++) {
    const charStr = string.charAt(i);
    const codeUnit = charStr.charCodeAt(0);
    result.push(
      (CBASE <= codeUnit && codeUnit < CTOP) ? fromCompatibility(codeUnit) :
      (SBASE <= codeUnit && codeUnit < STOP) ? decomposeSyllable(codeUnit) :
      charStr);
  }
  return result.join('');
}
Return Unicode characters as they are, except for Hangul characters, which
will be converted to the Conjoining Jamo form.

@param {string} string
@output {string}