Add keyboard event callback for Python passive viewer.

Fixes #766
Fixes #846

PiperOrigin-RevId: 549449372
Change-Id: I37d17f1162c66d0e8482d402aae22d9a16b59deb

python/mujoco/mjpython/mjpython.mm

@@ -115,12 +115,12 @@ class _MjPythonImpl(mujoco.viewer._MjPythonBase):
     self._termination = self.__class__.NOT_TERMINATED
     self._busy = False
 
-  def launch_on_ui_thread(self, model, data, handle_return):
+  def launch_on_ui_thread(self, model, data, handle_return, key_callback):
     with self._cond:
       if self._busy or self._task is not None:
         raise RuntimeError('another MuJoCo viewer is already open')
       else:
-        self._task = (model, data, handle_return)
+        self._task = (model, data, handle_return, key_callback)
         self._cond.notify()
 
   def terminate(self):
@@ -294,10 +294,11 @@ while True:
       break
 
     # Otherwise, launch the viewer.
-    model, data, handle_return = task
+    model, data, handle_return, key_callback = task
     ctypes.CDLL(None).mjpython_show_dock_icon()
     mujoco.viewer._launch_internal(
-        model, data, run_physics_thread=False, handle_return=handle_return)
+        model, data, run_physics_thread=False, handle_return=handle_return,
+        key_callback=key_callback)
     ctypes.CDLL(None).mjpython_hide_dock_icon()
 
   finally: