fix: allow rest parameters to follow multiple optional - or not - parameters

[oreilles]

Fixes #8601

Actually, managed to clean up the whole thing and make it work with every valid test case I could think of.

It's not pretty (it's not that bad either), but it works.
There's still a case it doesn't solve though, but I'm fairly confident we got time before someone actually goes for such thing.

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Latest commit: fda3524

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[Rich-Harris]

this is a thing of real beauty — thanks so much! absolutely fantastic