Support for getStaticPaths.fallback = false (#3600)
Adds support for `getStaticPaths` returning `{ fallback: false }` by
building out all static paths and checking whether the resolved path is
included in that list.
`buildStaticPaths` requires the `next.config.js` path, as well as other
config options such as locale. I created WEB-546 to track being able to
pass them to the handlers.
