`Option::unwrap` is now const (#20007)
Summary
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I noticed while working on #20006 that we had a custom `unwrap` function
for `Option`. This has been const on stable since 1.83
([docs](https://doc.rust-lang.org/std/option/enum.Option.html#method.unwrap),
[release notes](https://blog.rust-lang.org/2024/11/28/Rust-1.83.0/)), so
I think it's safe to use now. I grepped a bit for related todos and
found this one for `AsciiCharSet` but no others.
Test Plan
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Existing tests
