Previously dynamic component URLs were being resolved client-side in a weird way that only worked during dev. This change makes them handle during compilation, so it works in both (and improves readability of the dynamic import output).
* Add support for React components.
This adds support for react components via a new `extensions` config in astro.config.mjs. In the future we can extend this to do things like look at the import statements, as Snowpack does.
* Fix the tests
