[stable23] Avoid use of iconv to get rid of unicode

Using iconv for translit depends upon server configuration, locale, and
 PHP version. Using htmlentities instead to have a consistent behavior
 independent of configuration.

Signed-off-by: Côme Chilliet <come.chilliet@nextcloud.com>
Co-authored-by: MichaIng <micha@dietpi.com>