Add Visualization tab to simulate.

Also:
- Increased label width in mjUI tight theme spacing.
- Added `mjITEM_EDITFLOAT` for editing float values.
- Move mjUI numpad key codes to header file.
PiperOrigin-RevId: 535839953
Change-Id: Ibdc0a9a20be514caa5b487211212ed6f5b8a6ba9

src/user/user_model.cc

@@ -2897,6 +2897,11 @@ bool mjCModel::CopyBack(const mjModel* m) {
   option = m->opt;
   visual = m->vis;
 
+  // runtime-modifiable members of mjStatistic
+  meansize = m->stat.meansize;
+  extent = m->stat.extent;
+  mju_copy3(center, m->stat.center);
+
   // qpos0, qpos_spring
   for (int i=0; i<njnt; i++) {
     switch (joints[i]->type) {