_convertEventPosToPoint(e, p) {
    p.x = e.pageX - this.pswp.offset.x;
    p.y = e.pageY - this.pswp.offset.y;

    if ('pointerId' in e) {
      p.id = e.pointerId;
    } else if (e.identifier !== undefined) {
      p.id = e.identifier;
    }

    return p;
  }
Converts touch, pointer or mouse event
to PhotoSwipe point.

@private
@param {Touch | PointerEvent} e
@param {Point} p
@returns {Point}