Elements. Deprecate LocalElement.

Change-Id: Id0ee880a9fb98ecf7eb73d089039a985ec441dba
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/418915
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Paul Berry <[email protected]>

Author: scheglov

pkg/analyzer/api.txt

@@ -3414,7 +3414,7 @@ package:analyzer/dart/element/element.dart:
     effective (getter: Version)
     override (getter: Version?)
     package (getter: Version)
-  LocalElement (class extends Object implements Element):
+  LocalElement (class extends Object implements Element, deprecated):
     new (constructor: LocalElement Function())
   LocalVariableElement (class extends Object implements PromotableElement, deprecated):
     new (constructor: LocalVariableElement Function())

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

@@ -1811,10 +1811,10 @@ class LibraryLanguageVersion {
 }
 
 /// An element that can be (but is not required to be) defined within a method
-// ignore:deprecated_member_use_from_same_package
 /// or function (an [ExecutableElement]).
 ///
 /// Clients may not extend, implement or mix-in this class.
+@Deprecated('Use LocalElement2 instead')
 abstract class LocalElement implements Element {}
 
 /// A local variable.