SpreadJS: Implement Alt+Down key for List Validator Dropdowns

class.with.spreadsheet.js

const commandManager = workbook.commandManager();
commandManager.register('showListDown', () => openDropdown(sheet, workbook));
commandManager.setShortcutKey('showListDown', GC.Spread.Commands.Key.down, false, false, true);

spreadOpenDrowndown.js

import * as GC from '@grapecity/spread-sheets';

export const openDropdown = (sheet: GC.Spread.Sheets.Worksheet, workbook: GC.Spread.Sheets.Workbook) => {
  const row = sheet.getActiveRowIndex();
  const col = sheet.getActiveColumnIndex();
  const validator = sheet.getCell(row, col).validator();
  if (validator) {
    // if cell has data validator, show the list.
    const inputElement = workbook.getHost().getElementsByTagName('input')[0];
    if (inputElement) {
      inputElement.click();
    }
  }
};

Adapted from the code provided by Grapecity here: https://stackoverflow.com/a/55971587/5866637