function splitLongToH3Index(lower, upper) {
    return hexFrom32Bit(upper) + zeroPad(8, hexFrom32Bit(lower));
}
Get a H3 index string from a split long (pair of 32-bit ints)
@param  {number} lower Lower 32 bits
@param  {number} upper Upper 32 bits
@return {H3Index}       H3 index