Don't use DisplayName for topic reporting

[fierevere]

Another ticket related to empty/not set DisplayNames,
when such user reports a topic, its impossible to see who has reported topic without looking into source code

Example:

<li><a href="https://wordpress.org/support/users/koullis/"></a> on October 5, 2022 at 5:36 pm reason: you can delete it there is a reply in similar post</li>

in this topic: ​https://wordpress.org/support/topic/critical-vulnerability-4/?view=all

Generally there is no reason to use Display Names there, when topic is reported by other person than topic participants, moderators have to click on reporter's name to get their profile link just to get their username for
@-mention reply.

Perfect solution will be to completely remove usage of display name there and use username.

[fierevere]

setting prio to normal, as per Otto's explantation is not possible to set empty displaynames for new and existing profiles.

However, there are still such (old) profiles without displaynames and convenience issue for replying.

[fierevere]

Duplicate of #6500.