TokenIterator asks desugar'ers if they want to rewrite tokens by passing current and an option to peek ahead. They are then given the tokens themselves to rewrite as they please.
coverage: 90.075% (+1.6%) from 88.469%
when pulling c225a1fadebd2b4446b632e1d58663ca5306e63f on token-desugar
into 19000cbfd053d0639f329f130fff2e705ba298f2 on main.
TokenIterator asks desugar'ers if they want to rewrite tokens by passing current and an option to peek ahead. They are then given the tokens themselves to rewrite as they please.