Publish types for package

[achou11]

Having access to the the type definitions is helpful when you're programmatically working with the plugin. Considering this project is using TypeScript already, there are two paths:

1. Emit the type definitions as a build step
2. Write a manual definitions file

In the meantime, I have manually written definitions in https://github.com/achou11/webxdc-app-template/blob/main/types/webxdc__vite-plugins.d.ts in case it's helpful for anyone else. Happy to make a PR if helpful!

[Simon-Laux]

Yes, a PR would be very helpful and appreciated, I also encountered this today.