fix(ngSanitize): encode surrogate pair properly

The encodeEndities function encode non-alphanumeric characters to entities with charCodeAt.
charCodeAt does not return one value when their unicode codeponts is higher than 65,356.
It returns surrogate pair, and this is why the Emoji which has higher codepoints is garbled.
We need to handle them properly.

Closes #5088
Closes #6911

Author: memolog

src/ngSanitize/sanitize.js

@@ -161,6 +161,7 @@ var START_TAG_REGEXP =
   COMMENT_REGEXP = /<!--(.*?)-->/g,
   DOCTYPE_REGEXP = /<!DOCTYPE([^>]*?)>/i,
   CDATA_REGEXP = /<!\[CDATA\[(.*?)]]>/g,
+  SURROGATE_PAIR_REGEXP = /[\uD800-\uDBFF][\uDC00-\uDFFF]/g,
   // Match everything outside of normal chars and " (quote character)
   NON_ALPHANUMERIC_REGEXP = /([^\#-~| |!])/g;
 
@@ -399,6 +400,11 @@ function decodeEntities(value) {
 function encodeEntities(value) {
   return value.
     replace(/&/g, '&amp;').
+    replace(SURROGATE_PAIR_REGEXP, function (value) {
+      var hi = value.charCodeAt(0);
+      var low = value.charCodeAt(1);
+      return '&#' + (((hi - 0xD800) * 0x400) + (low - 0xDC00) + 0x10000) + ';';
+    }).
     replace(NON_ALPHANUMERIC_REGEXP, function(value){
       return '&#' + value.charCodeAt(0) + ';';
     }).

test/ngSanitize/sanitizeSpec.js

@@ -241,6 +241,11 @@ describe('HTML', function() {
       expect(html).toEqual('<div>');
     });
 
+    it('should handle surrogate pair', function() {
+      writer.chars(String.fromCharCode(55357, 56374));
+      expect(html).toEqual('&#128054;');
+    });
+
     describe('explicitly disallow', function() {
       it('should not allow attributes', function() {
         writer.start('div', {id:'a', name:'a', style:'a'});