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/controllers/categories_controller.rb

@@ -365,7 +365,7 @@ class CategoriesController < ApplicationController
         if SiteSetting.enable_category_group_moderation?
           params[:reviewable_by_group_id] = Group.where(
             name: params[:reviewable_by_group_name],
-          ).pluck_first(:id) if params[:reviewable_by_group_name]
+          ).pick(:id) if params[:reviewable_by_group_name]
         end
 
         result =