code: public float angle(Vector2fc v) {
          float dot = x*v.x() + y*v.y();
          float det = x*v.y() - y*v.x();
          return (float) Math.atan2(det, dot);
      }
docs: /* (non-Javadoc)
  @see org.joml.Vector2fc#angle(org.joml.Vector2fc)