fix: reimplement treeshaking non-dynamic prerendered remote functions

[teemingc]

This PR fixes a regression where prerendered remote functions were no longer treeshaken. It was accidentally removed in https://github.com/sveltejs/kit/pull/14293/changes#diff-6997ee961e0605b37d712e389f6a938a4ae080038f0ed9b9643894b287985feaL51 while we were trying to figure out how to make remote functions in node_modules work correctly.

It also ensures that these prerendered functions can't be called in production with arbitrary inputs. cc: @GauBen

EDIT: In retrospect, this doesn't help remove certain files if they aren’t in use by anyone after the treeshaking occurred.

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Latest commit: 25a685f

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[teemingc]

We probably need to fix up any sourcemaps too after the treeshaking

[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-15447-svelte.vercel.app/