Automated g4 rollback of changelist 604607692.

*** Reason for rollback ***

breakage resulting in "inertia must have positive eigenvalues" when parsing URDF's

*** Original change description ***

Move fullinertia from mjCAlternative to mjCBody.

***

PiperOrigin-RevId: 604677400
Change-Id: Iab8263b5b0aee310bd75404e314f3b707ce3300e

src/user/user_api.h

@@ -30,6 +30,7 @@ typedef struct _mjmOrientation {
   double xyaxes[6];               // x and y axes
   double zaxis[3];                // z axis (use minimal rotation)
   double euler[3];                // euler rotations
+  double fullinertia[6];          // non-axis-aligned inertia matrix
 } mjmOrientation;
 
 typedef struct _mjmSite {