Move AST implementation out of generated

pkg/analyzer/lib/src/generated/testing/ast_factory.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 analyzer.src.generated.testing.ast_factory;
 
+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/ast.dart';
 import 'package:analyzer/src/generated/scanner.dart';
 import 'package:analyzer/src/generated/testing/token_factory.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
 
 /**
  * The class `AstFactory` defines utility methods that can be used to create AST nodes. The
  * nodes that are created are complete in the sense that all of the tokens that would have been
  * associated with the nodes by a parser are also created, but the token stream is not constructed.
  * None of the nodes are resolved.
  *
@@ skipping 1237 matching lines @@
           expression,
           TokenFactory.tokenFromType(TokenType.SEMICOLON));
 
   static YieldStatement yieldStatement(Expression expression) =>
       new YieldStatement(
           TokenFactory.tokenFromTypeAndString(TokenType.IDENTIFIER, "yield"),
           null,
           expression,
           TokenFactory.tokenFromType(TokenType.SEMICOLON));
 }