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