Prefer ActionDispatch parameter parsing over Rack

They're not likely to ever differ in behaviour for any of this file's
assertions, but we want to be strict about only calling Rack's parser
when we intend to / cannot avoid it, and this is not that.

Author: matthewd

actionpack/test/journey/router_test.rb

@@ -494,7 +494,7 @@ def _generate(route_name, options, recall)
           end
           path = @route_set.path_for(options, route_name)
           uri = URI.parse path
-          params = Rack::Utils.parse_nested_query(uri.query).symbolize_keys
+          params = ActionDispatch::ParamBuilder.from_query_string(uri.query).symbolize_keys
           [uri.path, params]
         end