[code style] com_users frontend

This fixes all the code style issues on `com_users` frontend.

This PR requires 2 tests as I've been forced to modify code:

https://github.com/phproberto/joomla-cms/compare/joomla:staging...phproberto:users-frontend?expand=1#diff-cd009ab48167c723aade8808e600cb79L166
@phproberto Missing the since tag.