Move all tests using dart:io to a separate directory

tests/standalone/src/io/DirectoryInvalidArgumentsTest.dart

 // Copyright (c) 2012, 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");
 
 class DirectoryInvalidArgumentsTest {
   static void testFailingList(Directory d, var recursive) {
     int errors = 0;
     d.onError = (error) {
@@ skipping 28 matching lines @@
   }
 
   static void testMain() {
     testInvalidArguments();
   }
 }
 
 main() {
   DirectoryInvalidArgumentsTest.testMain();
 }