Save normalising transform applied to mesh assets in mjModel.mesh_{pos,quat}

Fixes #409

PiperOrigin-RevId: 564217402
Change-Id: I53ddeef4e343905021cd7852d548f6769c876474

src/user/user_objects.h

@@ -576,6 +576,8 @@ class mjCMesh: public mjCBase {
   void Compile(const mjVFS* vfs);                   // compiler
   double* GetPosPtr(mjtMeshType type);              // get position
   double* GetQuatPtr(mjtMeshType type);             // get orientation
+  double* GetOffsetPosPtr();                        // get position offset for geom
+  double* GetOffsetQuatPtr();                       // get orientation offset for geom
   double* GetInertiaBoxPtr(mjtMeshType type);       // get inertia box
   double& GetVolumeRef(mjtMeshType type);           // get volume
   void FitGeom(mjCGeom* geom, double* meshpos);     // approximate mesh with simple geom
@@ -639,6 +641,8 @@ class mjCMesh: public mjCBase {
   double pos_surface_[3];             // CoM position
   double quat_volume_[4];             // inertia orientation
   double quat_surface_[4];            // inertia orientation
+  double pos_[3];                     // translation applied to asset vertices
+  double quat_[4];                    // rotation applied to asset vertices
   double boxsz_volume_[3];            // half-sizes of equivalent inertia box (volume)
   double boxsz_surface_[3];           // half-sizes of equivalent inertia box (surface)
   double aabb_[6];                    // axis-aligned bounding box