Move mesh inertia specification from global <compiler> to <asset/mesh>.

Three options:
- Convex: Use convex hull
- Exact: Use exact geometry (requires watertight mesh)
- Legacy: Legacy approximation (deprecated)

Fixes #2152

PiperOrigin-RevId: 688949900
Change-Id: I4537f343db917195c6fd58d517b189d5ee3be1cd

src/user/user_objects.h

@@ -868,6 +868,7 @@ class mjCMesh: public mjCMesh_, private mjsMesh {
   const std::vector<float>& UserTexcoord() const { return spec_texcoord_; }
   const std::vector<int>& Face() const { return face_; }
   const std::vector<int>& UserFace() const { return spec_face_; }
+  mjtMeshInertia Inertia() const { return spec.inertia; }
 
   // setters
   void SetNeedHull(bool needhull) { needhull_ = needhull; }
@@ -945,8 +946,7 @@ class mjCMesh: public mjCMesh_, private mjsMesh {
   std::vector<unsigned char> num_face_vertices_;
 
   // compute the volume and center-of-mass of the mesh given the face center
-  void ComputeVolume(double CoM[3], mjtGeomInertia type, const double facecen[3],
-                     bool exactmeshinertia);
+  void ComputeVolume(double CoM[3], mjtGeomInertia gtype, const double facecen[3]);
 };