Add assist to convert child: to children: in Flutter new-exprs

pkg/analysis_server/lib/src/services/correction/assist.dart

Index: pkg/analysis_server/lib/src/services/correction/assist.dart
diff --git a/pkg/analysis_server/lib/src/services/correction/assist.dart b/pkg/analysis_server/lib/src/services/correction/assist.dart
index 3b8ea1c7550a4505b640da0bb459d90096c9ba81..71589504c3b2b2bf2ede4faaafbd9b56ff022fc7 100644
--- a/pkg/analysis_server/lib/src/services/correction/assist.dart
+++ b/pkg/analysis_server/lib/src/services/correction/assist.dart
@@ -83,6 +83,8 @@ class DartAssistKind {
       'CONVERT_DOCUMENTATION_INTO_LINE',
       30,
       "Convert into line documentation comment");
+  static const CONVERT_FLUTTER_CHILD =
+      const AssistKind('CONVERT_FLUTTER_CHILD', 30, "Convert to children:");
   static const CONVERT_INTO_BLOCK_BODY = const AssistKind(
       'CONVERT_INTO_BLOCK_BODY', 30, "Convert into block body");
   static const CONVERT_INTO_EXPRESSION_BODY = const AssistKind(
@@ -119,10 +121,10 @@ class DartAssistKind {
       "Join 'if' statement with outer 'if' statement");
   static const JOIN_VARIABLE_DECLARATION = const AssistKind(
       'JOIN_VARIABLE_DECLARATION', 30, "Join variable declaration");
-  static const MOVE_FLUTTER_WIDGET_DOWN = const AssistKind(
-      "MOVE_FLUTTER_WIDGET_DOWN", 30, "Move widget down");
-  static const MOVE_FLUTTER_WIDGET_UP = const AssistKind(
-      "MOVE_FLUTTER_WIDGET_UP", 30, "Move widget up");
+  static const MOVE_FLUTTER_WIDGET_DOWN =
+      const AssistKind("MOVE_FLUTTER_WIDGET_DOWN", 30, "Move widget down");
+  static const MOVE_FLUTTER_WIDGET_UP =
+      const AssistKind("MOVE_FLUTTER_WIDGET_UP", 30, "Move widget up");
   static const REPARENT_FLUTTER_LIST = const AssistKind(
       "REPARENT_FLUTTER_LIST", 30, "Wrap widget list with new widget");
   static const REPARENT_FLUTTER_WIDGET = const AssistKind(