[FR] Show full_name_display instead of username when @mentioned

[theriverman]

Please describe the problem / need you are trying to solve.
I'm always frustrated when a user is mentioned in the comments and I can't figure out who's that user without navigating to their profile page in a new tab because their username in the system is either a generated corporate id or something random they've picked.

Describe the feature or the improvement you'd like and what are you trying to achieve.
The new WYSIWYG editor works great. If I press @, it shows both the username and the full_name_display of each member. However, when I save the comment and it gets rendered, only the username is shown without telling the person's real name.

Additional context
I have implemented a solution to this problem 2.5yrs ago, but when you introduced the tgWysiwygService, it has been lost.

Though I'm not yet familiar with the new WYSIWYG service and how its rendered, I can give it a try and reimplement this solution if you're open to such contribution on this legacy track.

Also, I can see that you're migrating the codebase to Angular 10. Could you add this FR to that track's backlog, please?