Move kernel baseline tests to front_end.

pkg/front_end/test/fasta/casts.dart

-// Copyright (c) 2016, 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.
-
-main() {
-  print("" as String);
-  print(1 as int);
-  print(1.0 as double);
-
-  print("" is String);
-  print("" is int);
-  print("" is double);
-
-  print(1 is String);
-  print(1 is int);
-  print(1 is double);
-
-  print(1.0 is String);
-  print(1.0 is int);
-  print(1.0 is double);
-}