(WIP) fix: correctly mark :not selectors

[dummdidumm]

This is a start at trying to properly fix the matching behavior of :not selectors (#14168). I'm in favor of cancling the endeavour because in my opinion it's just too complicated to do correctly and will make the whole css-prune.js file a hot mess - frankly it already is very complicated, and this would boost that even further.

The idea is to recognize when we're in a :not selector to revert the "did not match" logic. That itself sounds easy enough, but doesn't suffice at all. There are loads of special cases, which all need extra code:

• if there's a :global(...) we're right now assuming "yeah it matches", but we can't assume "yeah it does not match" for :not, because it could.
• for everything with multiple options where we iterative over selectors we can't say "one of them matched, so :not does not apply", instead we also gotta keep track of "on of them did not match, so :not applies"
• for dynamic bits like class: or <svelte:element> we gotta assume it does match, even within :not
• probably many more cases I didn't think of right now

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[Rich-Harris]

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