Runtime disabling of actuators according to group.

Added `option-actuatorgroupdisable` attribute and associated `mjOption.disableactuator` integer bitfield, used to disable sets of actuators at runtime according to their group.

- The first 6 actuator groups are toggleable in the `simulate` viewer.
- Minor refactor and cleanup of actuator documentation.

https://youtu.be/H9qG9Zf2W44

Fixes #1092.

PiperOrigin-RevId: 578335600
Change-Id: I4cf663b90ea768e4380acfa2fe3b8c15c7cbb568

src/engine/engine_vis_visualize.c

@@ -1072,6 +1072,11 @@ void mjv_addGeoms(const mjModel* m, mjData* d, const mjvOption* vopt,
   if (vopt->flags[mjVIS_ACTUATOR] && (category & catmask)) {
     for (int i=0; i < m->nu; i++) {
       if (vopt->actuatorgroup[mjMAX(0, mjMIN(mjNGROUP-1, m->actuator_group[i]))]) {
+        // skip if disabled
+        if (mj_actuatorDisabled(m, i)) {
+          continue;
+        }
+
         // determine extended range
         mjtNum rng[3] = {-1, 0, +1};
         mjtNum rmin = -1, rmax = 1, act = 0;