Move scanner out of generated and clean up imports

pkg/analyzer/example/scanner_driver.dart

 #!/usr/bin/env dart
 // Copyright (c) 2013, 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.
 
 import 'dart:io';
 
-import 'package:analyzer/src/generated/scanner.dart';
+import 'package:analyzer/dart/ast/token.dart';
+import 'package:analyzer/src/dart/scanner/reader.dart';
+import 'package:analyzer/src/dart/scanner/scanner.dart';
 
 main(List<String> args) {
   print('working dir ${new File('.').resolveSymbolicLinksSync()}');
 
   if (args.length == 0) {
     print('Usage: scanner_driver [files_to_scan]');
     exit(0);
   }
 
   for (var arg in args) {
     _scan(new File(arg));
   }
 }
 
 _scan(File file) {
   var src = file.readAsStringSync();
   var reader = new CharSequenceReader(src);
   var scanner = new Scanner(null, reader, null);
   var token = scanner.tokenize();
   while (token.type != TokenType.EOF) {
     print(token);
     token = token.next;
   }
 }