Allow helpers to be deferred until the routes have been finalized

ActiveStorage::BaseController subclasses ActionController::Base.
ActionController::Base has an "inherited" hook set that includes the
routing helpers to any subclass of AC::Base.  Since
ActiveStorage::BaseController is a subclass of AC::Base, it will get
routing helpers included automatically.  Unfortunately, when the
framework is eagerly loaded, ActiveStorage::BaseController is loaded
*before* the applications routes are loaded which means it attempts to
include an "in flight" module so it gets an exception.

This commit allows a class that's interested in being extended with
routing helpers register itself such that when the routes are finalized,
it will get the helpers included.  If the routes are already finalized,
then the helpers get included immediately.

actionpack/lib/abstract_controller/railties/routes_helpers.rb

@@ -7,11 +7,8 @@ module AbstractController
         Module.new do
           define_method(:inherited) do |klass|
             super(klass)
-            if namespace = klass.parents.detect { |m| m.respond_to?(:railtie_routes_url_helpers) }
-              klass.include(namespace.railtie_routes_url_helpers(include_path_helpers))
-            else
-              klass.include(routes.url_helpers(include_path_helpers))
-            end
+
+            routes.include_helpers klass, include_path_helpers
           end
         end
       end

actionpack/lib/action_dispatch/routing/route_set.rb

@@ -379,6 +379,7 @@ module ActionDispatch
         @finalized                  = false
         @env_key                    = "ROUTES_#{object_id}_SCRIPT_NAME".freeze
         @url_helpers                = nil
+        @deferred_classes           = []
 
         @set    = Journey::Routes.new
         @router = Journey::Router.new @set
@@ -434,11 +435,32 @@ module ActionDispatch
       end
       private :eval_block
 
+      def include_helpers(klass, include_path_helpers)
+        if @finalized
+          include_helpers_now klass, include_path_helpers
+        else
+          @deferred_classes << [klass, include_path_helpers]
+        end
+      end
+
+      def include_helpers_now(klass, include_path_helpers)
+        if namespace = klass.parents.detect { |m| m.respond_to?(:railtie_routes_url_helpers) }
+          klass.include(namespace.railtie_routes_url_helpers(include_path_helpers))
+        else
+          klass.include(url_helpers(include_path_helpers))
+        end
+      end
+      private :include_helpers_now
+
       def finalize!
         return if @finalized
         @append.each { |blk| eval_block(blk) }
         @finalized = true
         @url_helpers = build_url_helper_module true
+        @deferred_classes.each { |klass, include_path_helpers|
+          include_helpers klass, include_path_helpers
+        }
+        @deferred_classes.clear
       end
 
       def clear!