setFromCoplanarPoints method
Implementation
Plane setFromCoplanarPoints(Vector3 a, Vector3 b, Vector3 c) {
  final normal =
      _vector1.sub2(c, b).cross(_vector2.sub2(a, b)).normalize();
  // Q: should an error be thrown if normal is zero (e.g. degenerate plane)?
  setFromNormalAndCoplanarPoint(normal, a);
  return this;
}