Elements. For LocalVariableFragment enclosingFragment can be anything, not only ExecutableFragment.

For example, here it is the top-level variable fragment.
```
final a = [for (final value in []) value * 2];
```

Change-Id: I0c09c890256b624a28c1d55fffbfd94f9431b83e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/398928
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>

Author: scheglov

pkg/analyzer/lib/dart/element/element2.dart

@@ -1816,9 +1816,6 @@ abstract class LocalVariableFragment
   @override
   LocalVariableElement2 get element;
 
-  @override
-  ExecutableFragment? get enclosingFragment;
-
   /// Whether the variable has an initializer at declaration.
   bool get hasInitializer;
 

pkg/analyzer/lib/src/dart/element/element.dart

@@ -7322,8 +7322,7 @@ class LocalVariableElementImpl extends NonParameterVariableElementImpl
   LocalVariableElement2 get element => _element2;
 
   @override
-  ExecutableFragment get enclosingFragment =>
-      enclosingElement3 as ExecutableFragment;
+  Fragment get enclosingFragment => enclosingElement3 as Fragment;
 
   @override
   String get identifier {