Add clock sensor type.

PiperOrigin-RevId: 459720950
Change-Id: Ibda48ae7dc4aa7be451a947a1c53d10a7eaf176b

doc/XMLreference.rst

@@ -5135,6 +5135,16 @@ at a specified body, in global coordinates.
 :at:`body`: :at-val:`string, required`
    Name of the body where the kinematic subtree is rooted.
 
+.. _sensor-clock:
+
+:el-prefix:`sensor/` **clock** (*)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This element creates sensor that returns the simulation time.
+
+:at:`name`, :at:`noise`, :at:`cutoff`, :at:`user`
+   See :ref:`CSensor`.
+
 .. _sensor-user:
 
 :el-prefix:`sensor/` **user** (*)

doc/changelog.rst

@@ -11,6 +11,7 @@ General
 - Added ``mjd_transitionFD`` to compute efficient finite difference approximations of the state-transition and
   control-transition matrices, :ref:`see here<derivatives>` for more details.
 - Added ``ctrl`` attribute to :ref:`keyframes<keyframe>`.
+- Added ``clock`` sensor which :ref:`measures time<sensor-clock>`.
 - Added visualisation groups to skins.
 - Added actuator visualisation for ``free`` and ``ball`` joints and for actuators with ``site`` transmission.
 - Added visualisation for actuator activations.