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

introspect/structs.py

@@ -8914,11 +8914,6 @@ STRUCTS: Mapping[str, StructDecl] = dict([
                  ),
                  doc='range of geom groups used to compute inertia',
              ),
-             StructFieldDecl(
-                 name='exactmeshinertia',
-                 type=ValueType(name='mjtByte'),
-                 doc='if false, use old formula',
-             ),
              StructFieldDecl(
                  name='alignfree',
                  type=ValueType(name='int'),
@@ -10291,6 +10286,11 @@ STRUCTS: Mapping[str, StructDecl] = dict([
                  ),
                  doc='rescale mesh',
              ),
+             StructFieldDecl(
+                 name='inertia',
+                 type=ValueType(name='mjtMeshInertia'),
+                 doc='inertia type (convex, legacy, exact)',
+             ),
              StructFieldDecl(
                  name='smoothnormal',
                  type=ValueType(name='mjtByte'),