Raycaster: Fixed Transfer function changes of shading var not updating lightmap.
Changing the TF of the shading variable would not update the lightmap, e.g. changing from a transparent TF to an opaque TF.
This MR addresses that, by calling the new function onChangeActorVariableTransferFunction
when a TF is changed for a variable.
This is used by the ray-caster to trigger a lightmap update.