Expose IsDuringPlay property for actors and scripts to use in scripting

Source/Engine/Content/Content.cpp

@@ -166,6 +166,9 @@ void ContentService::Dispose()
     // Save assets registry before engine closing
     Cache.Save();
 
+    // Flush objects (some asset-related objects/references may be pending to delete)
+    ObjectsRemovalService::Flush();
+
     // Unload all remaining assets
     {
         ScopeLock lock(AssetsLocker);

Source/Engine/Level/SceneObject.h

@@ -97,7 +97,7 @@ public:
     /// <summary>
     /// Determines whether object is during play (spawned/loaded and fully initialized).
     /// </summary>
-    FORCE_INLINE bool IsDuringPlay() const
+    API_PROPERTY() FORCE_INLINE bool IsDuringPlay() const
     {
         return (Flags & ObjectFlags::IsDuringPlay) != 0;
     }