message: Simplify mouse hover highlight tracking using mScrollArea
  Effectively the two previous checks combined were checking if the mouse
  was in the scroll area.
diff: @@ -210,15 +210,7 @@ void ListBox::onMouseMove(int x, int y, int /*relX*/, int /*relY*/)
  const auto point = NAS2D::Point{x, y};
  - // Ignore mouse motion events if the pointer isn't within the menu rect.
  - if (!rect().contains(point))
  - {
  - mCurrentHighlight = constants::NO_SELECTION;
  - return;
  - }
  -
  - // if the mouse is on the slider then the slider should handle that
  - if (mSlider.visible() && mSlider.rect().contains(point))
  + if (!mScrollArea.contains(point))
  {
  mCurrentHighlight = constants::NO_SELECTION;
  return;
  