Correct placement of metadata with named parameters

Bug: #54273
Change-Id: I541456bf052ff44bd210d0e265d4d1d70ca5211e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/340560
Reviewed-by: William Hesse <whesse@google.com>
Commit-Queue: Erik Ernst <eernst@google.com>
diff --git a/tools/spec_parser/Dart.g b/tools/spec_parser/Dart.g
index 492efe2..64feb04 100644
--- a/tools/spec_parser/Dart.g
+++ b/tools/spec_parser/Dart.g
@@ -379,7 +379,7 @@
     ;
 
 defaultNamedParameter
-    :    REQUIRED? normalFormalParameter ('=' expression)?
+    :    metadata REQUIRED? normalFormalParameterNoMetadata ('=' expression)?
     ;
 
 typeWithParameters