_getWidthToItem(item) {
      const isRTL = this.effectiveDir === "rtl";
      const ltrWidthToItem = item.offsetLeft - this.offsetLeft;
      if (isRTL) {
        const itemOffsetParent = item.offsetParent;
        // in RTL the total width is equal to difference of the parent container width and
        // how much is the item offset to the left minus its offsetWidth
        if (!itemOffsetParent) {
          return 0;
        }
        return itemOffsetParent.offsetWidth - item.offsetLeft - item.offsetWidth;
      }
      return ltrWidthToItem;
    }
Returns the total width to item excluding the item width
RTL/LTR aware
@private
@param {HTMLElement} item