Prepare to publish analyzer 0.39.12

R=brianwilkerson@google.com

Change-Id: Iea5b9186f6fe89f93b6a95fe2aa2b0045f8a4930
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/153381
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

Author: scheglov

pkg/analyzer/CHANGELOG.md

@@ -1,6 +1,10 @@
-## 0.39.12-dev
+## 0.39.12
 * Deprecated `canUseSummaries` in `DartSdkManager` constructor.
   Summaries are not supported this way for SDK.
+* Set uri for implicit dart:core import.
+* Add overrideKnownFeaturesAsync() for DartDoc testing.
+* Remove DartSdk.useSummary.
+* Move TypeSystemImpl to src/dart/element/type_system.dart
 
 ## 0.39.11
 * Deprecated `ClassElement.hasReferenceToSuper`.

pkg/analyzer/pubspec.yaml

@@ -1,5 +1,5 @@
 name: analyzer
-version: 0.39.12-dev
+version: 0.39.12
 description: This package provides a library that performs static analysis of Dart code.
 homepage: https://github.com/dart-lang/sdk/tree/master/pkg/analyzer