Add exports field

[thecrypticace]

Fixes #914

In most instances this isn't necessary except for SSR. And Vite even works around this problem for SSR bundles by doing some rewriting when the module is loaded. However, given that there are some places that need this it'll help make usage more consistent across environments.

You can no longer require() or import files directly from the package that are not covered by the exports field. However, all paths that were previously importable should be covered. We have covered the all components with and without an extension, the index file (with and without an extension), an implicit index export, legacy v1 imports, the package.json, etc…

[blowsie]

I beleive this commit breaks usage in nuxt3 with vite

[thecrypticace]

@blowsie can you open an issue with a reproduction please? It shouldn't be a breaking change.