DEV: Replace #pluck_first freedom patch with AR #pick in core (#19893)

The #pluck_first freedom patch, first introduced by @danielwaterworth has served us well, and is used widely throughout both core and plugins. It seems to have been a common enough use case that Rails 6 introduced it's own method #pick with the exact same implementation. This allows us to retire the freedom patch and switch over to the built-in ActiveRecord method.

There is no replacement for #pluck_first!, but a quick search shows we are using this in a very limited capacity, and in some cases incorrectly (by assuming a nil return rather than an exception), which can quite easily be replaced with #pick plus some extra handling.

app/serializers/suggested_topics_mixin.rb

@@ -33,7 +33,7 @@ module SuggestedTopicsMixin
           object.topic_allowed_group_ids,
           scope.user.id,
         )
-        .pluck_first(:name)
+        .pick(:name)
     end
   end
 

app/serializers/topic_view_serializer.rb

@@ -283,7 +283,7 @@ class TopicViewSerializer < ApplicationSerializer
           owner: true,
         },
       )
-      .pluck_first(:name)
+      .pick(:name)
   end
 
   def include_requested_group_name?