Use CommentRanges in backwards lexing (#7360)

## Summary

The tokenizer was split into a forward and a backwards tokenizer. The
backwards tokenizer uses the same names as the forwards ones (e.g.
`next_token`). The backwards tokenizer gets the comment ranges that we
already built to skip comments.

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Co-authored-by: Micha Reiser <micha@reiser.io>

crates/ruff_python_trivia/src/lib.rs

@@ -1,8 +1,10 @@
+mod comment_ranges;
 mod cursor;
 pub mod textwrap;
 mod tokenizer;
 mod whitespace;
 
+pub use comment_ranges::CommentRanges;
 pub use cursor::*;
 pub use tokenizer::*;
 pub use whitespace::*;