up
Gets the basis vector representing the Y-axis of the coordinate system after this matrix's transformation. This is commonly referred to as the "up" vector.
For a row-major matrix, this vector is extracted directly from the second row: (m10, m11, m12).
If the matrix includes scaling, this vector's length will reflect that scaling and it is not guaranteed to be a unit vector.
Return
A Vector3 representing the transformed Y-axis.