4868 mention inside tags

Fix for: #4868
Example: we have a user with name Olga and I write: "Hello Olga, how are you @olg" , after select username text transform to "Hello Olga, how are you Olga" for mention user script find first "Olga" in my post and add syntax tag, but I need to tag second 'Olga' text, for do this I add zero width character before name of user and mention text where find  "\u200B"+username
Sorry for my very bad English