Elements. Deprecate Element.children

Change-Id: I525184a8d855a111985d141c458738a2fddb2a2a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/418925
Reviewed-by: Paul Berry <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

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

@@ -416,7 +416,7 @@ abstract class Element implements AnalysisTarget {
   /// A list of this element's children.
   ///
   /// There is no guarantee of the order in which the children will be included.
-  @Deprecated('Use Element2 instead')
+  @Deprecated(elementModelDeprecationMsg)
   List<Element> get children;
 
   /// The analysis context in which this element is defined.