multiply method
- Vector4 arg
 
Multiply this by arg.
Implementation
void multiply(Vector4 arg) {
  final argStorage = arg._v4storage;
  _v4storage[3] *= argStorage[3];
  _v4storage[2] *= argStorage[2];
  _v4storage[1] *= argStorage[1];
  _v4storage[0] *= argStorage[0];
}