Upgrade `vite` to `2.8.x`, unvendoring `vite` and bringing Astro's dependencies up-to-date.
This is a low-level change that you shouldn't have to worry about too much, but it should fix many, many issues with CJS/ESM interoperability. It also allows Astro to stay up-to-date with the `vite` ecosystem. If you run into any unexpected problems, please let us know by opening an issue.