add backwards-compatible layer for old static route rules

[danielroe]

Currently with implementation of #946 we drop the static cache rule.

This is a breaking change for users who deploy to Vercel or Netlify and use the static or swr rules, as mentioned in #1124.

Because Nuxt has a caret version constraint, I would request that we add a layer for backwards compatibility in the next release, and would also suggest moving back to ~ constraint in Nuxt to allow features like this to be released in minors.

[pi0]

This is a good idea to keep converting swr to isr for a while while updating docs and communicating. But also as mentioned in the initial PR, this is not particularly a breaking change but fix breaking change as sometimes we have in Nuxt too :) SWR behavior will keep working on both platforms and also closer to what is expected.

Fix for static to isr makes sense btw.

[danielroe]

I wouldn't consider it a breaking fix. We even documented that swr and static were the way to implement ISR on Netlify + Vercel. But as long as we have backwards compatibility and don't remove until next major, I think it's totally fine.