Add user_init for setting default parameters.

PiperOrigin-RevId: 604942840
Change-Id: I746ac7bb28f508b606bc0b8544136f523ce50d4c

src/user/user_api.h

@@ -155,9 +155,18 @@ MJAPI void mjm_setDefault(mjElement element, void* defspec);
 // Set frame.
 MJAPI void mjm_setFrame(mjElement dest, void* frame);
 
-// Compute quat and inertia from body->fullinertia..
+// Compute quat and inertia from body->fullinertia.
 MJAPI const char* mjm_setFullInertia(mjmBody* body, double quat[4], double inertia[3]);
 
+
+//---------------------------------- Initialization functions --------------------------------------
+
+// Default body attributes.
+MJAPI void mjm_defaultBody(mjmBody& body);
+
+// Default site attributes.
+MJAPI void mjm_defaultSite(mjmSite& site);
+
 #ifdef __cplusplus
 }
 #endif