add AddListener helper for IL2CPP, cleanup some unity extensions

src/Helpers/EventHelper.cs

@@ -0,0 +1,33 @@
+#if CPP
+using System;
+using UnityEngine.Events;
+
+namespace UnityExplorer.Helpers
+{
+    // Possibly temporary, just so Il2Cpp can do the same style "AddListener" as Mono.
+    // Just saves me having a preprocessor directive for every single AddListener.
+
+    public static class EventHelper
+    {
+        public static void AddListener(this UnityEvent action, Action listener)
+        {
+            action.AddListener(listener);
+        }
+
+        public static void AddListener<T>(this UnityEvent<T> action, Action<T> listener)
+        {
+            action.AddListener(listener);
+        }
+
+        public static void AddListener<T0, T1>(this UnityEvent<T0, T1> action, Action<T0, T1> listener)
+        {
+            action.AddListener(listener);
+        }
+
+        public static void AddListener<T0, T1, T2>(this UnityEvent<T0, T1, T2> action, Action<T0, T1, T2> listener)
+        {
+            action.AddListener(listener);
+        }
+    }
+}
+#endif

src/Helpers/UnityHelpers.cs

@@ -18,12 +18,27 @@ namespace UnityExplorer.Helpers
             }
         }
 
-        public static string ActiveSceneName
+        public static bool IsNullOrDestroyed(this object obj, bool suppressWarning = false)
         {
-            get
+            var unityObj = obj as Object;
+            if (obj == null)
             {
-                return UnityEngine.SceneManagement.SceneManager.GetActiveScene().name;
+                if (!suppressWarning)
+                    ExplorerCore.LogWarning("The target instance is null!");
+
+                return true;
             }
+            else if (obj is Object)
+            {
+                if (!unityObj)
+                {
+                    if (!suppressWarning)
+                        ExplorerCore.LogWarning("The target UnityEngine.Object was destroyed!");
+
+                    return true;
+                }
+            }
+            return false;
         }
 
         public static string ToStringLong(this Vector3 vec)