Rebase onto multiple actuator branch. thanks yamato.

Author: surfnerd

com.unity.ml-agents.extensions/Runtime/Input/InputActuatorComponent.cs

@@ -44,14 +44,18 @@ void OnDisable()
             m_lastCreatedActuator?.CleanupActionAsset();
         }
 
-        public override IActuator CreateActuator()
+        public override IActuator[] CreateActuators()
         {
             FindNeededComponents();
             m_lastCreatedActuator?.ResetData();
             m_lastCreatedActuator = new InputActuator(m_PlayerInput, m_BehaviorParameters, m_Agent);
-            return m_lastCreatedActuator;
+            return new IActuator[] { m_lastCreatedActuator };
         }
 
+#pragma warning disable 672
+        public override IActuator CreateActuator() { return null; }
+#pragma warning restore 672
+
         public override ActionSpec ActionSpec => ActionSpec.MakeContinuous(0);
     }
 }