DEV: Include pending reviewables in the main tab in the user menu (#18471)

This commit makes pending reviewables show up in the main tab (a.k.a. "all notifications" tab). Pending reviewables along with unread notifications are always shown first and they're sorted based on their creation date (most recent comes first).

The dismiss button currently only shows up if there are unread notifications and it doesn't dismiss pending reviewables. We may follow up with another change soon that allows makes the dismiss button work with reviewables and remove them from the list without taking any action on them. 

Follow-up to 079450c9e4.

app/controllers/reviewables_controller.rb

@@ -71,9 +71,11 @@ class ReviewablesController < ApplicationController
   end
 
   def user_menu_list
-    reviewables = Reviewable.list_for(current_user, limit: 30, status: :pending).to_a
     json = {
-      reviewables: reviewables.map! { |r| r.basic_serializer.new(r, scope: guardian, root: nil).as_json }
+      reviewables: Reviewable.basic_serializers_for_list(
+        Reviewable.user_menu_list_for(current_user),
+        current_user
+      ).as_json
     }
     render_json_dump(json, rest_serializer: true)
   end