copyInto method
Copy this into arg.
Implementation
Matrix2 copyInto(Matrix2 arg) {
  final argStorage = arg._m2storage;
  argStorage[0] = _m2storage[0];
  argStorage[1] = _m2storage[1];
  argStorage[2] = _m2storage[2];
  argStorage[3] = _m2storage[3];
  return arg;
}