Develop barracuda 0.3.x (#2952)

* Removed Barracuda as drop-in library, added Barracuda package dependency

* Removed Google Protobuf library as now it comes with Barracuda package

* List<T>.Length seems to be extension, which is not available in .NET coming with Unity 2017, switched to .Count

.gitignore

 /UnitySDK/[Bb]uild/
 /UnitySDK/[Bb]uilds/
 /UnitySDK/[Pp]ackages/
-/UnitySDK/[Uu]nity[Pp]ackage[Mm]anager/
 /UnitySDK/Assets/AssetStoreTools*
 /UnitySDK/Assets/Plugins*
 /UnitySDK/Assets/Demonstrations*

UnitySDK/Assets/ML-Agents/Scripts/InferenceBrain/TensorApplier.cs

             {
                 var model = (Model)barracudaModel;
 
-                for (var i = 0; i < model?.memories.Length; i++)
+                for (var i = 0; i < model?.memories.Count; i++)
-                        new BarracudaMemoryOutputApplier(model.memories.Length, i, memories);
+                        new BarracudaMemoryOutputApplier(model.memories.Count, i, memories);
                 }
             }
         }

UnitySDK/Assets/ML-Agents/Scripts/InferenceBrain/TensorGenerator.cs

             if (barracudaModel != null)
             {
                 var model = (Model)barracudaModel;
-                for (var i = 0; i < model.memories.Length; i++)
+                for (var i = 0; i < model.memories.Count; i++)
                 {
                     m_Dict[model.memories[i].input] =
                         new BarracudaRecurrentInputGenerator(i, allocator, memories);

UnitySDK/UnityPackageManager/manifest.json

+{
+	"dependencies": {
+	"com.unity.barracuda": "0.3.2-preview"
+	}
+}

UnitySDK/Assets/ML-Agents/Plugins/ProtoBuffer/Google.Protobuf.dll.meta

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-  isPreloaded: 0
-  isOverridable: 0
-  platformData:
-  - first:
-      Any: 
-    second:
-      enabled: 1
-      settings: {}
-  - first:
-      Editor: Editor
-    second:
-      enabled: 0
-      settings:
-        DefaultValueInitialized: true
-  - first:
-      Windows Store Apps: WindowsStoreApps
-    second:
-      enabled: 0
-      settings:
-        CPU: AnyCPU
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: 

UnitySDK/Assets/ML-Agents/Plugins/Barracuda.Core.meta

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