Feature Request: Automatic Build Time Static Optimization

[benbot]

It'd be great if we had the same kind of build time static optimization that nextjs has https://nextjs.org/docs/advanced-features/automatic-static-optimization

We could probably just see if a page has a preload at build time and, if not, "export" that component to static or something like that.

Besides the performance gain, if someone was making a static site with sapper it would automatically export it to static which is kind of neat.

[jthegedus]

Regarding this feature, I would expect the output .html file to end up in the static folder to be pushed to the CDN with all other assets, though this makes subsequent builds messy as they would have to cleanup the generated files in static. Perhaps tracking them in the __sapper__/build/build.json manifest we would be able to cleanup the prior output files before generating the new build and manifest.

[benmccann]

Also requested in #1324