Stop using deprecated charCodeAt in Intl

pkg/intl/lib/number_format.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.
 
 library number_format;
 
 import 'dart:math';
 
 import "intl.dart";
 import "number_symbols.dart";
@@ skipping 240 matching lines @@
    */
   void _group(int totalLength, int position) {
     var distanceFromEnd = totalLength - position;
     if (distanceFromEnd <= 1 || _groupingSize <= 0) return;
     if (distanceFromEnd % _groupingSize == 1) {
       _add(symbols.GROUP_SEP);
     }
   }
 
   /** Returns the code point for the character '0'. */
-  int get _zero => '0'.charCodes[0];
+  int get _zero => '0'.codeUnits.first;
 
   /** Returns the code point for the locale's zero digit. */
-  int get _localeZero => symbols.ZERO_DIGIT.charCodeAt(0);
+  // Note that there is a slight risk of a locale's zero digit not fitting
+  // into a single code unit, but it seems very unlikely, and if it did,
+  // there's a pretty good chance that our assumptions about being able to do
+  // arithmetic on it would also be invalid.
+  int get _localeZero => symbols.ZERO_DIGIT.codeUnits.first;
 
   /**
    * Returns the prefix for [x] based on whether it's positive or negative.
    * In en_US this would be '' and '-' respectively.
    */
   String _signPrefix(num x) {
     return x.isNegative ? _negativePrefix : _positivePrefix;
   }
 
   /**
    * Returns the suffix for [x] based on wether it's positive or negative.
    * In en_US there are no suffixes for positive or negative.
    */
   String _signSuffix(num x) {
     return x.isNegative ? _negativeSuffix : _positiveSuffix;
   }
 }