[XRI3] [BUG] Spatial mouse manipulation are relative to scene origin instead of head pose

[AMollis]

To reproduce

Steps to reproduce the behavior:

1. Build sample from Features/XRI3 branch for HL2
2. On HL2 go to SpatialMouseSample.unity scene
3. Connect blue tooth mouse to scene.
4. Move away from origin (move to the left or right of scene content)
5. Select an object in scene, use mouse scroll wheel
6. Result 1: Content scrolls perpendicular to head gaze (left-right), instead of parallel to gaze (backward-forward)
7. Rotate scene content 90 degrees around y axis by grabbing description panel
8. Select an object, and move mouse up and down
9. Result 2: Content does seem to move correctly (also the mouse pointer has a hard time intersecting with scene content)

Expected behavior

1. Result 1: Content to scroll parallel to head gaze (backward-forward)
2. Result 2: Content to move up and down and can be targeted easily with mouse pointer.