[NUI] deprecate unused FocusRequestArgs class (#2411)

`FocusChangeREquested` event was removed in
https://github.com/Samsung/TizenFX/pull/903.

diff --git a/src/Tizen.NUI/src/public/BaseHandle.cs b/src/Tizen.NUI/src/public/BaseHandle.cs
index 1b601ba..009bc5a 100755 (executable)
--- a/src/Tizen.NUI/src/public/BaseHandle.cs
+++ b/src/Tizen.NUI/src/public/BaseHandle.cs
@@ -536,6 +536,7 @@ namespace Tizen.NUI
         /// <summary>
         /// Contains event arguments for the FocusChangeRequested event.
         /// </summary>
+        [Obsolete("Deprecated in API9; Will be removed in API11.")]
         public class FocusRequestArgs : EventArgs
         {