Eager load Journey Formatter cache

This cache is used when url_for is called without a named route (ie.
when it's called with hash options). Eager loading avoids building the
cache on the first call and potentially allows the memory to be shared
via CoW on forking servers.

actionpack/lib/action_dispatch/journey/formatter.rb

@@ -104,6 +104,11 @@ def clear
         @cache = nil
       end
 
+      def eager_load!
+        cache
+        nil
+      end
+
       private
         def extract_parameterized_parts(route, options, recall)
           parameterized_parts = recall.merge(options)

actionpack/lib/action_dispatch/routing/route_set.rb

@@ -386,6 +386,7 @@ def initialize(config = DEFAULT_CONFIG)
       def eager_load!
         router.eager_load!
         routes.each(&:eager_load!)
+        formatter.eager_load!
         nil
       end