approxPolyDP function
ApproxPolyDP approximates a polygonal curve(s) with the specified precision.
For further details, please see:
https:///docs.opencv.org/master/d3/dc0/group__imgproc__shape.html#ga0012a5fdaea70b8a9970165d98722b4c
Implementation
VecPoint approxPolyDP(VecPoint curve, double epsilon, bool closed) {
  final vec = VecPoint();
  cvRun(() => cimgproc.cv_approxPolyDP(curve.ref, epsilon, closed, vec.ptr, ffi.nullptr));
  return vec;
}