Revert "Revert "update focus_mangaer""

This reverts commit ac0e1bb5cc9e55af5f29b3e88ee238c54189abb7.

com.unity.uiwidgets/Runtime/widgets/focus_manager.cs

 
         public FocusAttachment _attachment;
 
-<<<<<<< HEAD
+
-=======
-        IEnumerable<FocusNode> descendants {
->>>>>>> parent of a10f14fb... Merge branch 'dev_1.17.5' into shiyun/skia
             get {
                 if (_descendants == null) {
                     List<FocusNode> result = new List<FocusNode>();