Update docs to pass doc validation. (#4953)

com.unity.ml-agents/Runtime/Actuators/ActionSpec.cs

         /// <param name="numContinuousActions">The number of continuous actions available.</param>
         /// <param name="discreteBranchSizes">The array of branch sizes for the discrete actions.  Each index
         /// contains the number of actions available for that branch.</param>
-        /// <returns>An ActionSpec initialized with the specified action sizes.</returns>
         public ActionSpec(int numContinuousActions = 0, int[] discreteBranchSizes = null)
         {
             m_NumContinuousActions = numContinuousActions;

com.unity.ml-agents/Runtime/Sensors/IBuiltInSensor.cs

     /// </summary>
     public enum BuiltInSensorType
     {
+        /// <summary>
+        /// Default Sensor type if it cannot be determined.
+        /// </summary>
+        /// <summary>
+        /// The Vector sensor used by the agent.
+        /// </summary>
-        // Note that StackingSensor actually returns the wrapped sensor's type
+        /// <summary>
+        /// The Stacking Sensor type. NOTE: StackingSensor actually returns the wrapped sensor's type.
+        /// </summary>
+        /// <summary>
+        /// The RayPerception Sensor types, both 3D and 2D.
+        /// </summary>
+        /// <summary>
+        /// The observable attribute sensor type.
+        /// </summary>
+        /// <summary>
+        /// Sensors that use the Camera for observations.
+        /// </summary>
+        /// <summary>
+        /// Sensors that use RenderTextures for observations.
+        /// </summary>
+        /// <summary>
+        /// Sensors that use buffers or tensors for observations.
+        /// </summary>
+        /// <summary>
+        /// The sensors that observe properties of rigid bodies.
+        /// </summary>
+        /// <summary>
+        /// The sensors that observe Match 3 boards.
+        /// </summary>
+        /// <summary>
+        /// Sensors that break down the world into a grid of colliders to observe an area at a pre-defined granularity.
+        /// </summary>
         GridSensor = 10
     }
 
         /// <returns>A BuiltInSensorType corresponding to the sensor.</returns>
         BuiltInSensorType GetBuiltInSensorType();
     }
-
-
 }

com.unity.ml-agents/Runtime/Sensors/ObservationWriter.cs

             }
         }
 
+        /// <summary>
+        /// Write the list of floats.
+        /// </summary>
+        /// <param name="data">The actual list of floats to write.</param>
+        /// <param name="writeOffset">Optional write offset to start writing from.</param>
         public void AddList(IList<float> data, int writeOffset = 0)
         {
             if (m_Data != null)
                     var val = data[index];
                     m_Data[index + m_Offset + writeOffset] = val;
-
                 }
             }
             else

com.unity.ml-agents/Runtime/SideChannels/TrainingAnalyticsSideChannel.cs

 
 namespace Unity.MLAgents.SideChannels
 {
+    /// <summary>
+    /// Side Channel implementation for recording which training features are being used.
+    /// </summary>
     public class TrainingAnalyticsSideChannel : SideChannel
     {
         const string k_TrainingAnalyticsConfigId = "b664a4a9-d86f-5a5f-95cb-e8353a7e8356";