New frontend example for react-router

[jimmyt857]

With the recent merge between React Router and Remix, React Router v7 is a compelling option as a frontend framework and I wanted to try it out. Sending a PR because I thought others might benefit from my attempt at getting this working within Bazel!

Although the dev and production versions of the server are both working, this example is 95% of the way there. Unfortunately I'm not yet deeply familiar with rules_js, rules_ts, or even react-router. I need a bit of help fixing the //react-router/app:app_typecheck and //react-router/app:test tests, they are each failing for a different reason:

• :app_typecheck fails because it is missing some special typing files generated by react-router. See their documentation here. I already wrapped the react-router typegen command into a js_run_binary but I couldn't figure out how to make the ts_library target accept the generated files as input.
• :test fails because the vite library somehow doesn't contain expect. Honestly not sure why this is happening, the test code is taken almost exactly from https://github.com/bazelbuild/examples/blob/main/frontend/react/src/App.test.tsx.