Added mjData.eq_active user input variable, for enabling/disabling the state of equality constraints.

Renamed `mjModel.eq_active` to `mjModel.eq_active0`, which now has the semantic of "initial value of `mjData.eq_active`".

Fixes #876.

PiperOrigin-RevId: 570410643
Change-Id: Id03171e751377c7cc453f143abee64239ee2e2ed

include/mujoco/mjvisualize.h

@@ -506,7 +506,6 @@ struct mjvSceneState_ {
     int* eq_type;
     int* eq_obj1id;
     int* eq_obj2id;
-    mjtByte* eq_active;
     mjtNum* eq_data;
 
     int* tendon_num;
@@ -564,6 +563,7 @@ struct mjvSceneState_ {
 
     mjtNum* ctrl;
     mjtNum* xfrc_applied;
+    mjtByte* eq_active;
 
     mjtNum* sensordata;