chore: add Node-agnostic utils

[teemingc]

splitting out changes from #15574

This PR creates and moves some utils to be Node-agnostic so that we can use them to resolve paths in the dev environment

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[teemingc]

Making this a draft because after re-examining why we need this, we could instead make it so that we resolve the paths outside the environment then communicate them back to the environment.

EDIT: might not be worth doing that just for some path resolving actually. We also still need path.relative to resolve paths synchronously at https://github.com/sveltejs/kit/pull/15574/changes#diff-d2344aa425f99c605f40fdf8ea76be2f063c21cafc0402e044b1a9a254f60e7dR210 . Marking this as ready

[teemingc]

This was always supposed to use the Vite root setting rather than '.' which is the same as process.cwd(). I just couldn't figure out how to pass the root setting here until now