Elements. Deprecate EnumElement.

Change-Id: I21b51cf2a0eff465dc9725a9477656b7ba2228ff
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/418828
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Paul Berry <paulberry@google.com>

pkg/analyzer/api.txt

@@ -3266,7 +3266,7 @@ package:analyzer/dart/element/element.dart:
     visitTopLevelVariableElement (method: R? Function(TopLevelVariableElement))
     visitTypeAliasElement (method: R? Function(TypeAliasElement))
     visitTypeParameterElement (method: R? Function(TypeParameterElement))
-  EnumElement (class extends Object implements InterfaceElement):
+  EnumElement (class extends Object implements InterfaceElement, deprecated):
     new (constructor: EnumElement Function())
   ExecutableElement (class extends Object implements FunctionTypedElement):
     new (constructor: ExecutableElement Function())

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

@@ -1089,6 +1089,7 @@ abstract class ElementVisitor<R> {
 /// An element that represents an enum.
 ///
 /// Clients may not extend, implement or mix-in this class.
+@Deprecated('Use EnumElement2 instead')
 abstract class EnumElement implements InterfaceElement {}
 
 /// An element representing an executable object, including functions, methods,

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

@@ -1186,6 +1186,7 @@ class CompilationUnitElementImpl extends UriReferencedElementImpl
     return null;
   }
 
+  @Deprecated(elementModelDeprecationMsg)
   @override
   EnumElement? getEnum(String name) {
     for (var element in enums) {
@@ -3513,7 +3514,10 @@ abstract class ElementOrMember {}
 
 /// An [InterfaceElementImpl] which is an enum.
 class EnumElementImpl extends InterfaceElementImpl
-    implements EnumElement, EnumFragment {
+    implements
+        // ignore:deprecated_member_use_from_same_package
+        EnumElement,
+        EnumFragment {
   late EnumElementImpl2 augmentedInternal;
 
   /// Initialize a newly created class element to have the given [name] at the
@@ -7334,6 +7338,7 @@ class LibraryElementImpl extends ElementImpl
     return _getElementByName(classes, name);
   }
 
+  @Deprecated(elementModelDeprecationMsg)
   EnumElement? getEnum(String name) {
     for (var unitElement in units) {
       var element = unitElement.getEnum(name);

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

@@ -308,18 +308,6 @@ extension ElementOrNullExtension on Element? {
   }
 }
 
-extension EnumElement2Extension on EnumElement2 {
-  EnumElement get asElement {
-    return firstFragment as EnumElement;
-  }
-}
-
-extension EnumElementExtension on EnumElement {
-  EnumElement2 get asElement2 {
-    return (this as EnumElementImpl).element;
-  }
-}
-
 extension EnumElementImplExtension on EnumElementImpl {
   EnumElementImpl2 get asElement2 {
     return element;