Move SdkExtUriResolver from analysis_server to analyzer so it can be used in analyzer_cli

pkg/analyzer/lib/source/sdk_ext.dart

Index: pkg/analyzer/lib/source/sdk_ext.dart
diff --git a/pkg/analysis_server/lib/src/sdk_ext.dart b/pkg/analyzer/lib/source/sdk_ext.dart
similarity index 99%
rename from pkg/analysis_server/lib/src/sdk_ext.dart
rename to pkg/analyzer/lib/source/sdk_ext.dart
index 86467e6973f1c950fc534355c2fcf03067599ce9..8b324dcc9c3e2e708623f265017114381f26c907 100644
--- a/pkg/analysis_server/lib/src/sdk_ext.dart
+++ b/pkg/analyzer/lib/source/sdk_ext.dart
@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-library analysis_server.src.sdk_ext;
+library source.sdk_ext;
 
 import 'dart:async';
 import 'dart:collection';