function getBaseCellNumber(h3Index) {
    const [lower, upper] = h3IndexToSplitLong(h3Index);
    return H3.getBaseCellNumber(lower, upper);
}
Get the number of the base cell for a given H3 index
@static
@param  {H3IndexInput} h3Index  H3 index to get the base cell for
@return {number}           Index of the base cell (0-121)