6599: Add attribute highlight modifier to all tokens inside attributes r=matklad a=Veykril
This has the side effect that we also emit `attribute.attribute` highlights now, as in, the tokens that get the attribute semantic type also get the attribute modifier. I personally don't think it's really a problem but maybe it is to some? It's just that it was really simple to implement it this way, which is why I just went this route for now.
Fixes#6536
Co-authored-by: Lukas Wirth <lukastw97@gmail.com>
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