clone function
Creates a new mat2 initialized with values from an existing matrix
@param {ReadonlyMat2} a matrix to clone @returns {mat2} a new 2x2 matrix
Implementation
List<double> clone(List<double> a) {
List<double> out = [];
out[0] = a[0];
out[1] = a[1];
out[2] = a[2];
out[3] = a[3];
return out;
}