Add VRChat and GitHub packages to Unity project

Assets/Udon/Editor/UdonImportPostProcessor.cs

@@ -0,0 +1,23 @@
+using System.IO;
+using UnityEditor;
+using UnityEngine;
+
+namespace VRC.Udon.Editor
+{
+    public class UdonImportPostProcessor : AssetPostprocessor
+    {
+        private const string PREFABS_INITIALIZED = "PrefabsInitialized";
+        
+        static void OnPostprocessAllAssets(string[] importedAssets, string[] deletedAssets, string[] movedAssets, string[] movedFromAssetPaths)
+        {
+            // Get key unique to this project, exit early if we've run the function already
+            string key = Path.Combine(Application.dataPath, PREFABS_INITIALIZED);
+            if (EditorPrefs.HasKey(key))
+                return;
+            
+            // Function never run for this project - compile and link all prefab programs
+            UdonEditorManager.PopulateAllPrefabSerializedProgramAssetReferences();
+            EditorPrefs.SetBool(key, true);
+        }
+    }
+}