Fix the offset of for-each statements that have an await (issue 35723)

Change-Id: Ifad641807a967a23c7d7e76d5e52f978beef32f4
Reviewed-on: https://dart-review.googlesource.com/c/90442
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
diff --git a/pkg/analyzer/lib/src/dart/ast/ast.dart b/pkg/analyzer/lib/src/dart/ast/ast.dart
index 7fd1355..75fcb2e 100644
--- a/pkg/analyzer/lib/src/dart/ast/ast.dart
+++ b/pkg/analyzer/lib/src/dart/ast/ast.dart
@@ -4903,7 +4903,7 @@
   }
 
   @override
-  Token get beginToken => forKeyword;
+  Token get beginToken => awaitKeyword ?? forKeyword;
 
   @override
   Statement get body => _body;