slerp VEX function

Quaternion blend between q1 and q2 based on the bias.

Contexts: image3d, chop, cop, pop, sop, surface, displace, fog, light, shadow, photon, cvex

  1. vector4 slerp(vector4 q1, vector4 q2, float bias)

Quaternion blend between q1 and q2 based on the bias.