New: Add interface-filtered object references

Add native hard and soft reference types for scene objects that implement
a scripting interface:

- ScriptingObjectInterfaceReference<T>
- SoftObjectInterfaceReference<T>

Source/Engine/Scripting/ScriptingObjectInterfaceReferenceUtils.h

@@ -0,0 +1,30 @@
+// Copyright (c) Wojciech Figat. All rights reserved.
+
+#pragma once
+
+#include "Engine/Scripting/ScriptingObjectReference.h"
+#include "Engine/Level/SceneObject.h"
+
+/// <summary>
+/// Utility methods for scene object interface references.
+/// </summary>
+/// <typeparam name="T">The type of the scripting interface.</typeparam>
+template<typename T>
+struct ScriptingObjectInterfaceReferenceHelper
+{
+    FORCE_INLINE static bool IsValidObject(const SceneObject* obj)
+    {
+        return !obj || obj->GetType().GetInterface(T::TypeInitializer) != nullptr;
+    }
+
+    FORCE_INLINE static SceneObject* GetSceneObject(T* interfaceObj)
+    {
+        return ScriptingObject::Cast<SceneObject>(ScriptingObject::FromInterface<T>(interfaceObj));
+    }
+
+    FORCE_INLINE static SceneObject* FindSceneObject(const Guid& id)
+    {
+        SceneObject* obj = static_cast<SceneObject*>(FindObject(id, SceneObject::GetStaticClass()));
+        return IsValidObject(obj) ? obj : nullptr;
+    }
+};