Replace use of NodeLocator2 in CorrectionProducer

This is the last use of NodeLocator2 outside of the analyzer package
itself that I'm aware of (at least in our code base).

Change-Id: I57ba74571d60e820c60e2ca3d8d17e9374597073
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/431440
Commit-Queue: Brian Wilkerson <[email protected]>
Reviewed-by: Samuel Rawlins <[email protected]>

Author: bwilkerson

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

@@ -126,7 +126,7 @@ class AddExplicitCast extends ResolvedCorrectionProducer {
   ({Expression target, DartType fromType, DartType toType})?
   _computeTargetAndTypes() {
     var target = coveringNode;
-    if (target is! Expression) {
+    if (target is! Expression || target.endToken.isSynthetic) {
       return null;
     }
 

pkg/analysis_server_plugin/lib/edit/dart/correction_producer.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:math' as math;
-
 import 'package:analysis_server_plugin/edit/correction_utils.dart';
 import 'package:analysis_server_plugin/edit/fix/dart_fix_context.dart';
 import 'package:analysis_server_plugin/src/utilities/selection.dart';
@@ -22,7 +20,6 @@ import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/source/source_range.dart';
 import 'package:analyzer/src/dart/analysis/session_helper.dart';
 import 'package:analyzer/src/dart/ast/ast.dart';
-import 'package:analyzer/src/dart/ast/utilities.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/inheritance_manager3.dart';
 import 'package:analyzer/src/dart/element/type.dart';
@@ -171,9 +168,8 @@ sealed class CorrectionProducer<T extends ParsedUnitResult>
     }
     var errorOffset = diagnostic.problemMessage.offset;
     var errorLength = diagnostic.problemMessage.length;
-    var endOffset = math.max(errorOffset + errorLength - 1, 0);
     return _coveringNode =
-        NodeLocator2(errorOffset, endOffset).searchWithin(unit);
+        unit.nodeCovering(offset: errorOffset, length: errorLength);
   }
 
   /// The length of the source range associated with the error message being