Deprecate the generated AST library and clean up imports

pkg/analyzer/test/src/abstract_single_unit.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // 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 test.services.src.index.abstract_single_file;
 
+import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
-import 'package:analyzer/src/generated/ast.dart';
+import 'package:analyzer/src/dart/ast/utilities.dart';
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:unittest/unittest.dart';
 
 import 'context/abstract_context.dart';
 
 class AbstractSingleUnitTest extends AbstractContextTest {
   bool verifyNoTestUnitErrors = true;
 
@@ skipping 81 matching lines @@
   void resolveTestUnit(String code) {
     addTestSource(code);
     testUnit = resolveLibraryUnit(testSource);
     if (verifyNoTestUnitErrors) {
       assertNoErrorsInSource(testSource);
     }
     testUnitElement = testUnit.element;
     testLibraryElement = testUnitElement.library;
   }
 }