Add built-in hemisphere mesh.

PiperOrigin-RevId: 791148546
Change-Id: Ic9ff0c9b0f5fa4fd22d5f7f848f150cf74d378ba

src/user/user_objects.h

@@ -1051,6 +1051,7 @@ class mjCMesh: public mjCMesh_, private mjsMesh {
   void NameSpace(const mjCModel* m);
 
   // make a mesh of a predefined shape
+  void MakeHemisphere(int res, bool make_faces, bool make_cap);
   void MakeWedge(int resolution[2], double fov[2], double gamma);
   void MakeRect(int resolution[2]);
   void MakeCone(int nedge, double radius);