[fix] util polyfill to make compiler self-contained

[dummdidumm]

this is needed for running the Svelte compiler in the browser again. Some package requires the builtin 'node' package which isn't bundled but also not available in the browser, so the REPL is broken. This slipped in through some dependency bump I guess.
Fixes #8010

I decided against using rollup-plugin-node-builtins because that one's quite outdated and ships a bunch of stuff we don't need

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