Light Linking: Support shadow linking to emissive meshes

This includes picking up a mesh emitter with the check for a fully
blocked light by a blocker with default linking configuration.

Implemented using an intersection loop, which might not have the
best performance compared to intersect-all behavior, but allows to
use some specialized for the shadow linking ray manipulations and
object flags check.

Ref #104972

@@ -483,6 +483,7 @@ ccl_device_forceinline bool mnee_newton_solver(KernelGlobals kg,
         if (!hit)
           break;
 
+        // TODO: Is the fetch needed here? The shade_surface simply reads isect->object.