Cycles: Align Camera data output between SVM and OSL

The `ZDepth` output of the camera data node was different between SVM
and OSL.

SVM would output the `ZDepth`, with negative distances for points
behind the camera. While OSL would output the absolute of the distance,
which resulted in points behind the camera becoming positive.

Align OSL to SVM and allow outputting the negative distance as it
allows users to differentiate between what's in front or behind the
camera.

Pull Request: https://projects.blender.org/blender/blender/pulls/132837

intern/cycles/kernel/osl/shaders/node_camera.osl

@@ -10,7 +10,7 @@ shader node_camera(output vector ViewVector = vector(0.0, 0.0, 0.0),
 {
   ViewVector = (vector)transform("world", "camera", P);
 
-  ViewZDepth = fabs(ViewVector[2]);
+  ViewZDepth = ViewVector[2];
   ViewDistance = length(ViewVector);
 
   ViewVector = normalize(ViewVector);