Explicitly specify actdim on PID plugin actuators, to allow them to be used with keyframes.

Support actdim attribute on plugin actuators.

Remove the actuator_actdim callback. This callback leads to crashes when loading keyframes for models that have a stateful plugin.

PiperOrigin-RevId: 650649505
Change-Id: I40d1994d02ae4e20ce631b2702a984766cf2628e

doc/XMLreference.rst

@@ -5666,6 +5666,8 @@ Associate this actuator with an :ref:`engine plugin<exPlugin>`. Either :at:`plug
 
 .. _actuator-plugin-user:
 
+.. _actuator-plugin-actdim:
+
 .. _actuator-plugin-dynprm:
 
 .. _actuator-plugin-actearly:
@@ -5673,7 +5675,7 @@ Associate this actuator with an :ref:`engine plugin<exPlugin>`. Either :at:`plug
 .. |actuator/plugin attrib list| replace:: :at:`name`, :at:`class`, :at:`group`, :at:`actlimited`, :at:`ctrllimited`,
    :at:`forcelimited`, :at:`ctrlrange`, :at:`forcerange`, :at:`lengthrange`, :at:`gear`, :at:`cranklength`,
    :at:`joint`, :at:`jointinparent`, :at:`site`, :at:`tendon`, :at:`cranksite`, :at:`slidersite`, :at:`user`,
-   :at:`dynprm`, :at:`actearly`
+   :at:`actdim`, :at:`dynprm`, :at:`actearly`
 
 |actuator/plugin attrib list|
    Same as in actuator/ :ref:`general <actuator-general>`.