Parse raw lifetimes #513
Description
In rust-lang/rust#126452, T-lang decided that we should treat 'r#lifetime as "raw lifetime" syntax and reserve 'prefix#lifetime, (retroactively) beginning in edition 2021 as an extension of the work around reserving identifier prefixes in Rust's RFC 3101.
This is mostly motivated by wanting to give users a way to move off of 'gen lifetimes since gen is a reserved keyword in edition 2024, and we don't allow keyword lifetimes in Rust.
Syn should probably handle this too.