Update reorderable_list.dart to use Dart 3 return switch statement fo…

…r consistency (#147505)

*Update `reorderable_list.dart` from `widgets` to use Dart 3 return switch statement syntax for consistency.*

This just a syntax change to match the rest of the functions in this file

packages/flutter/lib/src/widgets/reorderable_list.dart

@@ -1486,12 +1486,10 @@ double _sizeExtent(Size size, Axis scrollDirection) {
 }
 
 Size _extentSize(double extent, Axis scrollDirection) {
-  switch (scrollDirection) {
-    case Axis.horizontal:
-      return Size(extent, 0);
-    case Axis.vertical:
-      return Size(0, extent);
-  }
+  return switch (scrollDirection) {
+    Axis.horizontal => Size(extent, 0),
+    Axis.vertical => Size(0, extent),
+  };
 }
 
 double _offsetExtent(Offset offset, Axis scrollDirection) {