fix: Pass route data through window.Vaadin.routesConfig instead of an import

[Artur-]

Instead of importing routes.js/routes.ts/routes.tsx from the project into Flow.tsx and creating a circular dependency, this moves importing of routes.js to a new file that is always included when react is used vaadin-react.tsx. This file publishes the routes as window.Vaadin.routesConfig so that Flow.tsx can read them from there without directly depending on routes.js

Fixes #19658