DEV: Add plugin modifier locations for user search locations (#23169)

app/models/user_search.rb

@@ -198,7 +198,8 @@ class UserSearch
 
   def search
     ids = search_ids
-    return User.where("0=1") if ids.empty?
+    ids = DiscoursePluginRegistry.apply_modifier(:user_search_ids, ids)
+    return User.none if ids.empty?
 
     results =
       User.joins(

lib/search.rb

@@ -939,6 +939,8 @@ class Search
       users = users.where(suspended_at: nil)
     end
 
+    users = DiscoursePluginRegistry.apply_modifier(:search_user_search, users)
+
     users_custom_data_query =
       DB.query(<<~SQL, user_ids: users.pluck(:id), term: "%#{@original_term.downcase}%")
       SELECT user_custom_fields.user_id, user_fields.name, user_custom_fields.value FROM user_custom_fields