Blank characters stripping improvement in usernames

[Sama34]

It seems there are blank characters not being detected and stripped off of usernames, thus users are able to mask their usernames to look similar to usernames from other users.

Some example is the following :
https://www.fileformat.info/info/unicode...f/list.htm

We currently make some verifications or cleanup on trim_blank_chrs() in the verify_username() method but it seems to be lacking by now.

Original thread: Blank characters stripping improvement in usernames

[Sama34]

Some insight might be found in the following link :
https://stackoverflow.com/questions/23130740/determining-and-removing-invisible-characters-from-a-string-in-php-e2808e

[dvz]

Related: #2459