[NUI] Change TouchArea to TouchAreaOffset (#2948)

[NUI] Change  TouchArea to TouchAreaOffset (#2948)

    You can expand the touch area.

    for example)
      View view = new View();
      view.Size = new Size(10, 10);
      view.TouchEvent += OnTouch;
      view.TouchAreaOffset = new Offset(-100, 100, 100, -100); // left, right, bottom, top

    then touch area is 210x210.
    this is view.width  -touchAreaOffset.left + touchAreaOffset.right
    and view.height + touchAreaOffset.bottom  -touchAreaOffset.top