change default barracuda behavior (#5175)

com.unity.ml-agents/CHANGELOG.md

 - Added ML-Agents package settings. (#5027)
 - Make com.unity.modules.unityanalytics an optional dependency. (#5109)
 - Make com.unity.modules.physics and com.unity.modules.physics2d optional dependencies. (#5112)
+- The default `InferenceDevice` is now `InferenceDevice.Default`, which is equivalent to `InferenceDevice.Burst`. If you
+depend on the previous behavior, you can explicitly set the Agent's `InferenceDevice` to `InferenceDevice.CPU`. (#5175)
+
 #### ml-agents / ml-agents-envs / gym-unity (Python)
 
 ### Bug Fixes

com.unity.ml-agents/Runtime/Agent.cs

         public void SetModel(
             string behaviorName,
             NNModel model,
-            InferenceDevice inferenceDevice = InferenceDevice.CPU)
+            InferenceDevice inferenceDevice = InferenceDevice.Default)
         {
             if (behaviorName == m_PolicyFactory.BehaviorName &&
                 model == m_PolicyFactory.Model &&

com.unity.ml-agents/Runtime/Inference/ModelRunner.cs

                     case InferenceDevice.Burst:
                         executionDevice = WorkerFactory.Type.CSharpBurst;
                         break;
+                    case InferenceDevice.Default: // fallthrough
                     default:
                         executionDevice = WorkerFactory.Type.CSharpBurst;
                         break;

com.unity.ml-agents/Runtime/Policies/BarracudaPolicy.cs

     public enum InferenceDevice
     {
         /// <summary>
-        /// CPU inference. Corresponds to in WorkerFactory.Type.CSharp Barracuda.
-        /// Burst is recommended instead; this is kept for legacy compatibility.
+        /// Default inference. This is currently the same as Burst, but may change in the future.
-        CPU = 0,
+        Default = 0,
 
         /// <summary>
         /// GPU inference. Corresponds to WorkerFactory.Type.ComputePrecompiled in Barracuda.
         /// CPU inference using Burst. Corresponds to WorkerFactory.Type.CSharpBurst in Barracuda.
         /// </summary>
         Burst = 2,
+
+        /// <summary>
+        /// CPU inference. Corresponds to in WorkerFactory.Type.CSharp Barracuda.
+        /// Burst is recommended instead; this is kept for legacy compatibility.
+        /// </summary>
+        CPU = 3,
     }
 
     /// <summary>

com.unity.ml-agents/Runtime/Policies/BehaviorParameters.cs

         }
 
         [HideInInspector, SerializeField]
-        InferenceDevice m_InferenceDevice = InferenceDevice.Burst;
+        InferenceDevice m_InferenceDevice = InferenceDevice.Default;
 
         /// <summary>
         /// How inference is performed for this Agent's model.