Elements. Migrate FindElement2.

Change-Id: Ia5b901fbe8a7666a829628dcf9056c35e99f20bd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/396460
Reviewed-by: Phil Quitslund <pquitslund@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

pkg/analyzer/analyzer_use_new_elements.txt

@@ -160,7 +160,6 @@ lib/src/summary2/types_builder.dart
 lib/src/summary2/variance_builder.dart
 lib/src/task/strong_mode.dart
 lib/src/test_utilities/find_element.dart
-lib/src/test_utilities/find_element2.dart
 lib/src/test_utilities/find_node.dart
 lib/src/test_utilities/mock_sdk_elements.dart
 lib/src/util/ast_data_extractor.dart

pkg/analyzer/lib/dart/element/element.dart

@@ -546,6 +546,10 @@ abstract class DirectiveUriWithSource extends DirectiveUriWithRelativeUri {
 ///
 /// Clients may not extend, implement or mix-in this class.
 abstract class DirectiveUriWithUnit extends DirectiveUriWithSource {
+  /// The library fragment referenced by the [source].
+  @experimental
+  LibraryFragment get libraryFragment;
+
   /// The unit referenced by the [source].
   CompilationUnitElement get unit;
 }

pkg/analyzer/lib/dart/element/element2.dart

@@ -52,7 +52,6 @@ import 'package:analyzer/dart/constant/value.dart';
 import 'package:analyzer/dart/element/element.dart'
     show
         DirectiveUri,
-        DirectiveUriWithUnit,
         ElementAnnotation,
         ElementKind,
         ElementLocation,
@@ -2582,8 +2581,3 @@ abstract class VariableFragment implements Fragment {
   @override
   VariableFragment? get previousFragment;
 }
-
-extension DirectiveUriWithUnitExtension on DirectiveUriWithUnit {
-  /// The library fragment associated with this directive.
-  LibraryFragment get libraryFragment => unit as LibraryFragment;
-}

pkg/analyzer/lib/src/dart/element/element.dart

@@ -1913,6 +1913,9 @@ class DirectiveUriWithUnitImpl extends DirectiveUriWithRelativeUriImpl
     required this.unit,
   });
 
+  @override
+  LibraryFragment get libraryFragment => unit;
+
   @override
   Source get source => unit.source;
 }

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

@@ -35,6 +35,7 @@ bool _isOldModelElement(Element2? element) {
         'DirectiveUriWithRelativeUri',
         'DirectiveUriWithRelativeUriString',
         'DirectiveUriWithSource',
+        'DirectiveUriWithUnit',
         'ElementAnnotation',
         'ElementKind',
         'ElementLocation',