Add optional sign to Geometry Proximity result to indicate which face side is compared to

Distance is a positive number. This means the minus sign can be used for something else. The distance could be negated depending on the face orientation of the target. If e.g. two planes intersect, the calculated proximity will be positive for all points on one side of the intersection and negative on the other.

I'm not sure if this addition can benefit from the work already done. If not, this option is a bad idea. (Looking at the code there is not much evidence for reuse of work except iteration over all points. But ... I'm not a blender expert.)