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

include/mujoco/mjspec.h

@@ -57,11 +57,18 @@ extern "C" {
 //-------------------------------- enum types (mjt) ------------------------------------------------
 
 typedef enum mjtGeomInertia_ {     // type of inertia inference
-  mjINERTIA_VOLUME,                // mass distributed in the volume
+  mjINERTIA_VOLUME = 0,            // mass distributed in the volume
   mjINERTIA_SHELL,                 // mass distributed on the surface
 } mjtGeomInertia;
 
 
+typedef enum mjtMeshInertia_ {     // type of mesh inertia
+  mjINERTIA_CONVEX = 0,            // convex mesh inertia
+  mjINERTIA_EXACT,                 // exact mesh inertia
+  mjINERTIA_LEGACY,                // legacy mesh inertia
+} mjtMeshInertia;
+
+
 typedef enum mjtBuiltin_ {         // type of built-in procedural texture
   mjBUILTIN_NONE = 0,              // no built-in texture
   mjBUILTIN_GRADIENT,              // gradient: rgb1->rgb2
@@ -136,7 +143,6 @@ typedef struct mjSpec_ {           // model specification
   mjtByte fusestatic;              // fuse static bodies with parent
   int inertiafromgeom;             // use geom inertias (mjtInertiaFromGeom)
   int inertiagrouprange[2];        // range of geom groups used to compute inertia
-  mjtByte exactmeshinertia;        // if false, use old formula
   int alignfree;                   // align free joints with inertial frame
   mjLROpt LRopt;                   // options for lengthrange computation
 
@@ -447,6 +453,7 @@ typedef struct mjsMesh_ {          // mesh specification
   double refpos[3];                // reference position
   double refquat[4];               // reference orientation
   double scale[3];                 // rescale mesh
+  mjtMeshInertia inertia;          // inertia type (convex, legacy, exact)
   mjtByte smoothnormal;            // do not exclude large-angle faces from normals
   int maxhullvert;                 // maximum vertex count for the convex hull
   mjFloatVec* uservert;            // user vertex data