Clear and concise description of the problem

There is an API incompatibility with rollup for the addWatchFile api.
Specifically the first note after the addWatchFile documentation mentions the following:

Using this.addWatchFile from within the transform hook will make sure the transform hook is also reevaluated for this module if the watched file changes.

In Vite this.addWatchFile does nothing special in this case and just tracks the new file independently.

Suggested solution

Ideally we'd mirror the rollup behavior.