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

simulate/simulate.h

@@ -153,6 +153,7 @@ class Simulate {
     bool ui_update_rendering;
     bool ui_update_joint;
     bool ui_update_ctrl;
+    bool ui_remake_ctrl;
   } pending_ = {};
 
   SimulateMutex mtx;
@@ -228,6 +229,7 @@ class Simulate {
   // physics: need sync
   int disable[mjNDISABLE] = {0};
   int enable[mjNENABLE] = {0};
+  int enableactuator[mjNGROUP] = {0};
 
   // rendering: need sync
   int camera = 0;