Flat Routes fixes and improvements

[ryanflorence]

PR: https://github.com/remix-run/remix/pull/5228

[ryanflorence]

add route.js since folks are confused by folder imports with node module resolution

[kiliman]

Be careful. Once you go down that rabbit hole, it's hard to go back.

Yeah, differentiating between index routes and an index file in a folder can be a little confusing to the uninitiated.

[ryanflorence]

@ryanflorence to give a thumbs up

[zifahm]

thumbs down, I support the remix-flat-route convensions