_swapValues() {
      const affectedValue = this._valueAffected;
      if (!affectedValue) {
        return;
      }
      if (affectedValue === "startValue" && this.startValue > this.endValue) {
        const prevEndValue = this.endValue;
        this.endValue = this.startValue;
        this.startValue = prevEndValue;
      }
      if (affectedValue === "endValue" && this.endValue < this.startValue) {
        const prevStartValue = this.startValue;
        this.startValue = this.endValue;
        this.endValue = prevStartValue;
      }
      this._setValuesAreReversed();
      this._updateHandlesAndRange(this[affectedValue]);
      this.focusInnerElement();
      this.syncUIAndState();
    }
Swaps the start and end values of the handles if one came accros the other:
- If the start value is greater than the endValue swap them and their handles
- If the endValue become less than the start value swap them and their handles

Switches the focus to the opposite of the currently focused handle.

Note: Only the property values are reversed, the DOM elements of the handles
corresponding to them are never switched.

@private