How to use the @angular/material/core._countGroupLabelsBeforeOption function in @angular/material

private _scrollToOption(): void {
    const index = this.autocomplete._keyManager.activeItemIndex || 0;
    const labelCount = _countGroupLabelsBeforeOption(index,
        this.autocomplete.options, this.autocomplete.optionGroups);

    if (index === 0 && labelCount === 1) {
      // If we've got one group label before the option and we're at the top option,
      // scroll the list to the top. This is better UX than scrolling the list to the
      // top of the option, because it allows the user to read the top group's label.
      this.autocomplete._setScrollTop(0);
    } else {
      const newScrollPosition = _getOptionScrollPosition(
        index + labelCount,
        AUTOCOMPLETE_OPTION_HEIGHT,
        this.autocomplete._getScrollTop(),
        AUTOCOMPLETE_PANEL_HEIGHT
      );

      this.autocomplete._setScrollTop(newScrollPosition);

private _calculateOverlayPosition(): void {
    const itemHeight = this._getItemHeight();
    const items = this._getItemCount();
    const panelHeight = Math.min(items * itemHeight, SELECT_PANEL_MAX_HEIGHT);
    const scrollContainerHeight = items * itemHeight;

    // The farthest the panel can be scrolled before it hits the bottom
    const maxScroll = scrollContainerHeight - panelHeight;

    // If no value is selected we open the popup to the first item.
    let selectedOptionOffset =
        this.empty ? 0 : this._getOptionIndex(this._selectionModel.selected[0])!;

    selectedOptionOffset += _countGroupLabelsBeforeOption(selectedOptionOffset, this.options,
        this.optionGroups);

    // We must maintain a scroll buffer so the selected option will be scrolled to the
    // center of the overlay panel rather than the top.
    const scrollBuffer = panelHeight / 2;
    this._scrollTop = this._calculateOverlayScroll(selectedOptionOffset, scrollBuffer, maxScroll);
    this._offsetY = this._calculateOverlayOffsetY(selectedOptionOffset, scrollBuffer, maxScroll);

    this._checkOverlayWithinViewport(maxScroll);
  }

private _scrollActiveOptionIntoView(): void {
    const activeOptionIndex = this._keyManager.activeItemIndex || 0;
    const labelCount = _countGroupLabelsBeforeOption(activeOptionIndex, this.options,
        this.optionGroups);

    this.panel.nativeElement.scrollTop = _getOptionScrollPosition(
      activeOptionIndex + labelCount,
      this._getItemHeight(),
      this.panel.nativeElement.scrollTop,
      SELECT_PANEL_MAX_HEIGHT
    );
  }