Add [SdfLib](https://github.com/UPC-ViRVIG/SdfLib) plugin to first-party SDFs.

The following dependencies are disabled with a cmake patch file.
- Enoki
- OpenMP
- Assimp
- FCPW

PiperOrigin-RevId: 565352386
Change-Id: Icff9de68408e0afa2032bb83b24491fc4e41d181

src/engine/engine_collision_sdf.c

@@ -367,7 +367,9 @@ static mjtNum stepGradient(mjtNum x[3], const mjModel* m, const mjSDF* s,
     mjc_gradient(m, d, s, grad, x);
 
     // sanity check
-    if (isnan(grad[0]) || isnan(grad[1]) || isnan(grad[2])) {
+    if (isnan(grad[0]) || grad[0]>mjMAXVAL || grad[0]<-mjMAXVAL ||
+        isnan(grad[1]) || grad[1]>mjMAXVAL || grad[1]<-mjMAXVAL ||
+        isnan(grad[2]) || grad[2]>mjMAXVAL || grad[2]<-mjMAXVAL) {
       return mjMAXVAL;
     }
 

src/engine/engine_ray.c

@@ -774,6 +774,9 @@ mjtNum ray_sdf(const mjModel* m, const mjData* d, int g,
     if (distance < 1e-8) {
       return distance_total;
     }
+    if (distance > 1e6) {
+      break;
+    }
   }
 
   // reset counter