This combines the rotations of two quaternions into this.
The operation is not commutative so the order is important because AxB != BxA. Cogl follows the standard convention for quaternions here
so the rotations are applied right to left. This is similar to the combining of matrices.
<note>It is possible to multiply the a quaternion in-place, so this can be equal to
a but can't be equal to b.</note>
| this |
The destination Quaternion |
| left |
The second Quaternion rotation to apply |
| right |
The first Quaternion rotation to apply |