[NUI] Add widget list for keeping widget instance

same to this patch
https://github.com/Samsung/TizenFX/pull/5583

diff --git a/src/Tizen.NUI/src/public/Widget/Widget.cs b/src/Tizen.NUI/src/public/Widget/Widget.cs
index a10d238..ce65cb5 100755 (executable)
--- a/src/Tizen.NUI/src/public/Widget/Widget.cs
+++ b/src/Tizen.NUI/src/public/Widget/Widget.cs
@@ -46,6 +46,8 @@ namespace Tizen.NUI
             widgetImpl.WidgetInstanceResumed += OnWidgetInstanceResumed;
             widgetImpl.WidgetInstanceResized += OnWidgetInstanceResized;
             widgetImpl.WidgetInstanceUpdated += OnWidgetInstanceUpdated;
+
+            (WidgetApplication.Instance as WidgetApplication)?.AddWidgetInstance(this);
         }
 
         internal Widget(global::System.IntPtr cPtr, bool cMemoryOwn) : base(cPtr, cMemoryOwn)