Elements. Add AnnotatableElementImpl.

Use it for ManifestItem.match(), to highlight that matching is done
for implementation classes, and not for members.

Change-Id: I26d1843a9b8b24fbfcecc753dca1e3a19095a45e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/421963
Reviewed-by: Paul Berry <paulberry@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

Author: scheglov

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

@@ -69,6 +69,9 @@ abstract class AnnotatableElement implements Element2, Annotatable {
   MetadataImpl get metadata2;
 }
 
+abstract class AnnotatableElementImpl
+    implements ElementImpl2, AnnotatableElement {}
+
 @Deprecated('This is an internal class, do not use it')
 // TODO(scheglov): remove it when DartDoc stops using it
 // https://github.com/dart-lang/dartdoc/issues/4015
@@ -3841,7 +3844,7 @@ abstract class ExecutableElementImpl extends _ExistingElementImpl
 }
 
 abstract class ExecutableElementImpl2 extends FunctionTypedElementImpl2
-    implements ExecutableElement2OrMember {
+    implements ExecutableElement2OrMember, AnnotatableElementImpl {
   @override
   ExecutableElementImpl2 get baseElement => this;
 
@@ -5762,7 +5765,10 @@ abstract class InstanceElementImpl extends _ExistingElementImpl
 }
 
 abstract class InstanceElementImpl2 extends ElementImpl2
-    implements InstanceElement2, TypeParameterizedElement2, AnnotatableElement {
+    implements
+        InstanceElement2,
+        TypeParameterizedElement2,
+        AnnotatableElementImpl {
   @override
   InstanceElement2 get baseElement => this;
 

pkg/analyzer/lib/src/fine/manifest_item.dart

@@ -469,7 +469,7 @@ sealed class ManifestItem {
   });
 
   @mustCallSuper
-  bool match(MatchContext context, AnnotatableElement element) {
+  bool match(MatchContext context, AnnotatableElementImpl element) {
     return metadata.match(context, element.effectiveMetadata);
   }
 
@@ -711,9 +711,9 @@ enum _ManifestItemKind2 {
   interfaceConstructor,
 }
 
-extension _AnnotatableElementExtension on AnnotatableElement {
+extension _AnnotatableElementExtension on AnnotatableElementImpl {
   MetadataImpl get effectiveMetadata {
-    if (this case PropertyAccessorElement2OrMember accessor) {
+    if (this case PropertyAccessorElementImpl2 accessor) {
       return accessor.thisOrVariableMetadata;
     }
     return metadata2;
@@ -738,7 +738,7 @@ extension _GetterElementImplExtension on GetterElementImpl {
   }
 }
 
-extension _PropertyAccessExtension on PropertyAccessorElement2OrMember {
+extension _PropertyAccessExtension on PropertyAccessorElementImpl2 {
   MetadataImpl get thisOrVariableMetadata {
     if (isSynthetic) {
       return variable3!.metadata2;