rotate method
Implementation
Point<double> rotate(num radians) {
if (radians != 0.0) {
final cosTheta = cos(radians);
final sinTheta = sin(radians);
final nx = (cosTheta * x) + (sinTheta * y);
final ny = (cosTheta * y) - (sinTheta * x);
return Point<double>(nx, ny);
}
return toDoublePoint();
}