Rewrite (if possible) or provide alternatives to parenthesized_range and parentheses_iterator that take &Tokens as arguments instead of the CommentRanges, and don't use SimpleTokenizer or BackwardsTokenizer at all.

The ultimate goal of this would be to optimize calls sites such as this one in ty (which uses parentheses_iterator).

Suggested by @MichaReiser here: #21476 (comment)