Add VRChat and GitHub packages to Unity project

Assets/VRCSDK/Dependencies/VRChat/Editor/BuildPipeline/Samples/VRCSDKBuildRequestedCallbackSample.cs

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+#if VRC_SDK_PIPELINE_SAMPLES
+
+using UnityEditor;
+
+namespace VRC.SDKBase.Editor.BuildPipeline.Samples
+{
+    public class VRCSDKBuildRequestedCallbackSample : IVRCSDKBuildRequestedCallback
+    {
+        public int callbackOrder => 0;
+
+        public bool OnBuildRequested(VRCSDKRequestedBuildType requestedBuildType)
+        {
+            return EditorUtility.DisplayDialog("Build Confirmation", "Are you sure you want to build?", "Yes", "Not Yes");
+        }
+    }
+}
+
+#endif

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