[element model] migrate always_put_required_named_parameters_first

Bug: https://github.com/dart-lang/linter/issues/5099
Change-Id: I21e9a684b803704b315d3fd1671c919c6cddc138
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/387359
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>

Author: pq

pkg/linter/lib/src/rules/always_put_required_named_parameters_first.dart

@@ -38,7 +38,7 @@ class _Visitor extends SimpleAstVisitor<void> {
   void visitFormalParameterList(FormalParameterList node) {
     var nonRequiredSeen = false;
     for (var param in node.parameters.where((p) => p.isNamed)) {
-      var element = param.declaredElement;
+      var element = param.declaredFragment?.element;
       if (element != null && (element.hasRequired || element.isRequiredNamed)) {
         if (nonRequiredSeen) {
           var name = param.name;