Clarify direction range of XR_FACE_EXPRESSION2_EYES_LOOK_* blend shapes #188
Description
FB_face_tracking2 defines the eye look direction as a series of blend shapes to apply onto a model. These blend shapes are defined as a normalized 0-1 (are they allowed to go over 1? not explicitly specified seemingly...). But it's not defined anywhere what "1" means in terms of the amount of degrees of eye rotation.
Some software using this extension seems to imply it lines up 1:1 with unified expressions, and in use, this mapping apparently lines up. It's not defined clearly in the main unified expression documentation what "1" means either, however in a GitHub thread, it is clarified to be angle_of_rotation = arctan(normalized_value).
This should be stated in the spec, or if arctan isn't the correct conversion, the real range should be described.