FEATURE: Mention @here to notify users in topic (PR #14900)

Should we just be using Topic.visible_post_types here?

O I see we only want to consider regular and whisper posts.

I think we have a bug here:

[4] pry(main)> SiteSetting.min_trust_level_for_here_mention.to_s
=> "2"
[5] pry(main)> SiteSetting.min_trust_level_for_here_mention.to_i
=> 2

It seems like SiteSetting.min_trust_level_for_here_mention defaults to "2" so it’ll never match 'admin' or 'staff'

  describe "#can_mention_here?" do

O my bad, the site setting is an enum and can be set to ‘admin’`

It was a pleasure to review this :+1: PR looking good to merge.