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

pkg/analyzer_experimental/lib/src/utils.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 utils;
 
 import 'dart:io';
-import 'dart:uri';
 
 import 'package:pathos/path.dart' as pathos;
 
 /// Converts a local path string to a `file:` [Uri].
 Uri pathToFileUri(String pathString) {
   pathString = pathos.absolute(pathString);
   if (Platform.operatingSystem != 'windows') {
     return Uri.parse('file://$pathString');
   } else if (pathos.rootPrefix(pathString).startsWith('\\\\')) {
     // Network paths become "file://hostname/path/to/file".
     return Uri.parse('file:${pathString.replaceAll("\\", "/")}');
   } else {
     // Drive-letter paths become "file:///C:/path/to/file".
     return Uri.parse('file:///${pathString.replaceAll("\\", "/")}');
   }
 }