Report HintCode.UNUSED_FIELD for fields which are referenced in constructor field initializers.

pkg/analyzer/lib/src/dart/ast/ast.dart

Index: pkg/analyzer/lib/src/dart/ast/ast.dart
diff --git a/pkg/analyzer/lib/src/dart/ast/ast.dart b/pkg/analyzer/lib/src/dart/ast/ast.dart
index 19ed168401d3f05d6b5b47d46315303baa059cf7..97defa61517fef5041fa2e061c9cc2750fb57ff9 100644
--- a/pkg/analyzer/lib/src/dart/ast/ast.dart
+++ b/pkg/analyzer/lib/src/dart/ast/ast.dart
@@ -9043,6 +9043,10 @@ class SimpleIdentifierImpl extends IdentifierImpl implements SimpleIdentifier {
         return false;
       }
     }
+    if (parent is ConstructorFieldInitializer &&
+        identical(parent.fieldName, target)) {
+      return false;
+    }
     if (parent is ForEachStatement) {
       if (identical(parent.identifier, target)) {
         return false;