migrate raw string to new syntax in core

lib/coreimpl/date.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.
 
 class DateImplementation implements Date {
   final int millisecondsSinceEpoch;
   final bool isUtc;
 
   factory DateImplementation.fromString(String formattedString) {
     // Read in (a subset of) ISO 8601.
     // Examples:
     //    - "2012-02-27 13:27:00"
     //    - "2012-02-27 13:27:00.423z"
     //    - "20120227 13:27:00"
     //    - "20120227T132700"
     //    - "20120227"
     //    - "2012-02-27T14Z"
     //    - "-123450101 00:00:00 Z"  // In the year -12345.
     final RegExp re = const RegExp(
-        @'^([+-]?\d?\d\d\d\d)-?(\d\d)-?(\d\d)'  // The day part.
-        @'(?:[ T](\d\d)(?::?(\d\d)(?::?(\d\d)(.\d{1,6})?)?)? ?([zZ])?)?$');
+        r'^([+-]?\d?\d\d\d\d)-?(\d\d)-?(\d\d)'  // The day part.
+        r'(?:[ T](\d\d)(?::?(\d\d)(?::?(\d\d)(.\d{1,6})?)?)? ?([zZ])?)?$');
     Match match = re.firstMatch(formattedString);
     if (match !== null) {
       int parseIntOrZero(String matched) {
         // TODO(floitsch): we should not need to test against the empty string.
         if (matched === null || matched == "") return 0;
         return int.parse(matched);
       }
 
       double parseDoubleOrZero(String matched) {
         // TODO(floitsch): we should not need to test against the empty string.
@@ skipping 144 matching lines @@
   external Duration get timeZoneOffset;
   external int get year;
   external int get month;
   external int get day;
   external int get hour;
   external int get minute;
   external int get second;
   external int get millisecond;
   external int get weekday;
 }