Add mjmBody and mjmPlugin and their compiler C APIs.

PiperOrigin-RevId: 604937231
Change-Id: Ib8a2105ce6c0500d6a610258b46f192d9e73169d

src/xml/xml_urdf.h

@@ -19,6 +19,7 @@
 #include <unordered_set>
 #include <vector>
 
+#include "user/user_api.h"
 #include "user/user_model.h"
 #include "xml/xml_base.h"
 #include "tinyxml2.h"
@@ -52,7 +53,7 @@ class mjXURDF : public mjXBase {
   void Body(tinyxml2::XMLElement* body_elem);                      // parse body
   void Joint(tinyxml2::XMLElement* joint_elem);                    // parse joint
   mjCGeom* Geom(tinyxml2::XMLElement* geom_elem,
-                mjCBody* pbody, bool collision);      // parse origin and geometry of geom
+                mjmBody* pbody, bool collision);      // parse origin and geometry of geom
   void Origin(tinyxml2::XMLElement* origin_elem, double* pos, double* quat); // parse origin element
 
   void MakeMaterials(tinyxml2::XMLElement* elem);     // find all materials recursively