Merge the dart:uri library into dart:core and update the Uri class

pkg/stack_trace/test/trace_test.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.
 
 library trace_test;
 
 import 'dart:io';
-import 'dart:uri';
 
 import 'package:pathos/path.dart' as path;
 import 'package:stack_trace/src/utils.dart';
 import 'package:stack_trace/stack_trace.dart';
 import 'package:unittest/unittest.dart';
 
 String getStackTraceString() {
   try {
     throw '';
   } catch (_, stackTrace) {
@@ skipping 127 matching lines @@
 
     var folded = trace.foldFrames((frame) => frame.member.startsWith('foo'));
     expect(folded.toString(), equals('''
 foo.dart 42:21    notFoo
 foo.dart 1:100    fooBottom
 bar.dart 10:20    alsoNotFoo
 dart:async-patch  fooBottom
 '''));
   });
 }