How to use the @lumino/keyboard.getKeyboardLayout function in @lumino/keyboard

if (item && item.type === 'submenu') {
        this.triggerActiveItem();
      } else {
        this.rootMenu._menuRequested.emit('next');
      }
      return;
    }

    // Down Arrow
    if (kc === 40) {
      this.activateNextItem();
      return;
    }

    // Get the pressed key character.
    let key = getKeyboardLayout().keyForKeydownEvent(event);

    // Bail if the key is not valid.
    if (!key) {
      return;
    }

    // Search for the next best matching mnemonic item.
    let start = this._activeIndex + 1;
    let result = Private.findMnemonic(this._items, key, start);

    // Handle the requested mnemonic based on the search results.
    // If exactly one mnemonic is matched, that item is triggered.
    // Otherwise, the next mnemonic is activated if available,
    // followed by the auto mnemonic if available.
    if (result.index !== -1 && !result.multiple) {
      this.activeIndex = result.index;

let i = this._activeIndex;
      let n = this._menus.length;
      this.activeIndex = i === 0 ? n - 1 : i - 1;
      return;
    }

    // Right Arrow
    if (kc === 39) {
      let i = this._activeIndex;
      let n = this._menus.length;
      this.activeIndex = i === n - 1 ? 0 : i + 1;
      return;
    }

    // Get the pressed key character.
    let key = getKeyboardLayout().keyForKeydownEvent(event);

    // Bail if the key is not valid.
    if (!key) {
      return;
    }

    // Search for the next best matching mnemonic item.
    let start = this._activeIndex + 1;
    let result = Private.findMnemonic(this._menus, key, start);

    // Handle the requested mnemonic based on the search results.
    // If exactly one mnemonic is matched, that menu is opened.
    // Otherwise, the next mnemonic is activated if available,
    // followed by the auto mnemonic if available.
    if (result.index !== -1 && !result.multiple) {
      this.activeIndex = result.index;

function keystrokeForKeydownEvent(event: KeyboardEvent): string {
    let key = getKeyboardLayout().keyForKeydownEvent(event);
    if (!key) {
      return '';
    }
    let mods = '';
    if (event.ctrlKey) {
      mods += 'Ctrl ';
    }
    if (event.altKey) {
      mods += 'Alt ';
    }
    if (event.shiftKey) {
      mods += 'Shift ';
    }
    if (event.metaKey && Platform.IS_MAC) {
      mods += 'Cmd ';
    }

onKeyDown(grid: DataGrid, event: KeyboardEvent): void {
    switch (getKeyboardLayout().keyForKeydownEvent(event)) {
    case 'ArrowLeft':
      this.onArrowLeft(grid, event);
      break;
    case 'ArrowRight':
      this.onArrowRight(grid, event);
      break;
    case 'ArrowUp':
      this.onArrowUp(grid, event);
      break;
    case 'ArrowDown':
      this.onArrowDown(grid, event);
      break;
    case 'PageUp':
      this.onPageUp(grid, event);
      break;
    case 'PageDown':