DEV: Prioritize full name when display_name_on_posts active (#16078)

See: https://meta.discourse.org/t/display-full-name-not-username-when-attributing-quote-or-reply/203533?u=isaacjanzen for context

The initial release [broke quoting](https://meta.discourse.org/t/quoting-broken-when-name-matches-username/217633?u=isaacjanzen) but we now pass the username when 
```
siteSettings.display_name_on_posts && !siteSettings.prioritize_username_in_ux && post.name
```
as well as the full name to guarantee that we are not getting any mismatches when querying for user / avatar.

eg. 
```
[quote="Isaac Janzen, post:3, topic:7, full:true, username:isaac.janzen"]
bing bong
[/quote]
```

app/serializers/post_serializer.rb

@@ -257,6 +257,7 @@ class PostSerializer < BasicPostSerializer
   def reply_to_user
     {
       username: object.reply_to_user.username,
+      name: object.reply_to_user.name,
       avatar_template: object.reply_to_user.avatar_template
     }
   end