static <A> void forEachWithPosition(Matrix<A> m, IVF3<Int, Int, A> f) {
  if (m == null || f == null) ret;
  int w = m.getWidth(), h = m.getHeight();
  for y to h:
    for x to w:
      f.get(x, y, m.get(x, y));
}

Began life as a copy of #1022895