Add material namespacing to sites.

Fixes #2243.

PiperOrigin-RevId: 699713625
Change-Id: I1b45e43f2a6ccfa64c46489c9426fcc2acdc94c3

src/user/user_objects.h

@@ -615,6 +615,7 @@ class mjCSite : public mjCSite_, private mjsSite {
   void Compile(void);                     // compiler
   void CopyFromSpec();                    // copy spec into attributes
   void PointToLocal(void);
+  void NameSpace(const mjCModel* m);
 };