function isHighSurrogate(codePoint) {
    return codePoint >= HIGH_SURROGATE_START && codePoint <= HIGH_SURROGATE_END;
  }
Checks if `codePoint` is a high-surrogate number from range 0xD800 to 0xDBFF.

@ignore
@param {number} codePoint The code point number to be verified
@return {boolean} Returns a boolean whether `codePoint` is a high-surrogate number.