[ssr] Async route definition isn't compatible with SSR mode

[JounQin]

Version

4.0.0-beta.12

Reproduction link

https://github.com/JounQin/serverless-study/blob/master/src/router.ts#L11

Steps to reproduce

1. run yarn dev, works as expected with .then(Comp => Comp.default)
2. remove .then(Comp => Comp.default), [Vue warn]: Component is missing template or render function. will be logged from @vue/server-renderer, and no route content will be server rendered, and client side route will do the job

What is expected?

Without .then(Comp => Comp.default), the async route on sever should also work

What is actually happening?

Inconsistent between client and server

[JounQin]

Seems related to: vitejs/vite#764

[posva]

This is an upstream bug as commented in the linked issue. I added a test at 65c18db

[JounQin]

@posva The test case seems different, the issue is caused by Promise<{default: Component}>.