_updateValueOnRangeDrag(event) {
      // Calculate the new 'start' and 'end' values from the offset between the original press point and the current position of the mouse
      const ctor = this.constructor;
      const currentPageXPos = ctor.getPageXValueFromEvent(event);
      const newValues = this._calculateRangeOffset(currentPageXPos, this._initialStartHandlePageX);
      // No matter the which value is set as the one to be modified (by prev. user action) we want to modify both of them
      this._setAffectedValue(undefined);
      // Update the UI and the state according to the calculated new values
      this.update(undefined, newValues[0], newValues[1]);
    }
Updates UI and state when dragging of the whole selected range

@private