Change light attentuation for GIProbes
Created by: clayjohn
Fixes: https://github.com/godotengine/godot/issues/35200
From my understanding, we are taking a dot product between the cell normal and the light direction to easily exclude certain surfaces. However, it seems the normal and light direction are either in very different spaces or the normal is completely broken. Either way, starting with an attenuation
of 1.0
results in accurate lighting.
Because I don't totally understand why the current approach is broken, this will need @reduz's approval before merging.