tblGetCellName(cellEl, pad = 3) {
    return cellEl.getAttribute("data-col-name") ?? `C${String(cellEl.cellIndex + 1).padStart(pad, "0")}`;
  }
Return a standardised table cell name. Either from a `data-col-name` attribute or a numeric reference like `C003`
@param {HTMLTableCellElement} cellEl The cell element to process
@param {number=} pad Optional, default=3. Will be used to front-pad unnamed column references with zeros. e.g. 3 => "C002"/"C012"/"C342"
@returns {string} A cell name