Update mac and linux native and managed libraries. Fix shutdown issues. Delete link.xml.

com.unity.ml-agents/Plugins/ProtoBuffer/runtimes/osx/native/libgrpc_csharp_ext.bundle.meta

   iconMap: {}
   executionOrder: {}
   defineConstraints: []
-  isPreloaded: 0
+  isPreloaded: 1
   isOverridable: 0
   isExplicitlyReferenced: 0
   validateReferences: 1
         Exclude OSXIntel: 0
         Exclude OSXIntel64: 0
         Exclude OSXUniversal: 0
-        Exclude Win: 1
-        Exclude Win64: 1
+        Exclude Win: 0
+        Exclude Win64: 0
         Exclude iOS: 1
   - first:
       : OSXIntel
     second:
       enabled: 1
       settings:
-        CPU: x86_64
+        CPU: AnyCPU
         DefaultValueInitialized: true
         OS: OSX
   - first:
     second:
       enabled: 0
       settings:
-        CPU: AnyCPU
+        CPU: None
   - first:
       Standalone: LinuxUniversal
     second:
     second:
       enabled: 1
       settings:
-        CPU: AnyCPU
+        CPU: x86_64
-      enabled: 0
+      enabled: 1
-        CPU: AnyCPU
+        CPU: None
-      enabled: 0
+      enabled: 1
-        CPU: AnyCPU
+        CPU: None
   - first:
       iPhone: iOS
     second:

com.unity.ml-agents/Runtime/Communicator/RpcCommunicator.cs

 #define MLA_SUPPORTED_TRAINING_PLATFORM
 #endif
 
-# if MLA_SUPPORTED_TRAINING_PLATFORM
+#if MLA_SUPPORTED_TRAINING_PLATFORM
 using Grpc.Core;
 #if UNITY_EDITOR
 using UnityEditor;
 
             UpdateEnvironmentWithInput(input.RlInput);
             initParametersOut = initializationInput.RlInitializationInput.ToUnityRLInitParameters();
+            // Be sure to shut down the grpc channel when the application is quitting.
+            Application.quitting += NotifyQuitAndShutDownChannel;
             return true;
 #else
             initParametersOut = new UnityRLInitParameters();
             if (result.Header.Status != 200 || inputMessage.Header.Status != 200)
             {
                 m_IsOpen = false;
-                QuitCommandReceived?.Invoke();
+                NotifyQuitAndShutDownChannel();
+        void NotifyQuitAndShutDownChannel()
+        {
+            QuitCommandReceived?.Invoke();
+            m_Channel.ShutdownAsync().Wait();
+        }
+
 #endregion
 
 #region Destruction
             try
             {
                 m_Client.Exchange(WrapMessage(null, 400));
-                m_Channel.ShutdownAsync().Wait();
                 m_IsOpen = false;
             }
             catch
             {
                 case CommandProto.Quit:
                     {
-                        QuitCommandReceived?.Invoke();
+                        NotifyQuitAndShutDownChannel();
                         return;
                     }
                 case CommandProto.Reset:
                 // Not sure if the quit command is actually sent when a
                 // non 200 message is received.  Notify that we are indeed
                 // quitting.
-                QuitCommandReceived?.Invoke();
+                NotifyQuitAndShutDownChannel();
                 return message.UnityInput;
             }
             catch (Exception ex)
                 }
 
                 m_IsOpen = false;
-                QuitCommandReceived?.Invoke();
+                NotifyQuitAndShutDownChannel();
                 return null;
             }
         }

com.unity.ml-agents/Plugins/ProtoBuffer/link.xml

-<?xml version="1.0" encoding="utf-8"?>
-<linker>
-<!--
-Prevents Managed code stripping from removing code necessary for training.
-You may wish to disable this preservation (that is, re-enable code stripping) to
-reduce code size if you no longer need training. 
-See also https://docs.unity3d.com/Manual/ManagedCodeStripping.html
--->
-    <assembly fullname="Grpc.Core" preserve="all"/>
-</linker>

com.unity.ml-agents/Plugins/ProtoBuffer/link.xml.meta

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-guid: f94355fa6eab94c2d8529747b92ca3e1
-TextScriptImporter:
-  externalObjects: {}
-  userData: 
-  assetBundleName: 
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