pkg/(unit)test: include a copy of old matcher

lib/src/matcher.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.
+
+/// Support for specifying test expectations, such as for unit tests.
+library matcher;
+
+export 'matcher/core_matchers.dart';
+export 'matcher/description.dart';
+export 'matcher/error_matchers.dart';
+export 'matcher/expect.dart';
+export 'matcher/future_matchers.dart';
+export 'matcher/interfaces.dart';
+export 'matcher/iterable_matchers.dart';
+export 'matcher/map_matchers.dart';
+export 'matcher/numeric_matchers.dart';
+export 'matcher/operator_matchers.dart';
+export 'matcher/prints_matcher.dart';
+export 'matcher/string_matchers.dart';
+export 'matcher/throws_matcher.dart';
+export 'matcher/throws_matchers.dart';
+export 'matcher/util.dart';