69ac07608e
Make some Ordering methods const Resubmission of [PR#75463](https://github.com/rust-lang/rust/pull/75463) as per [PR#76172](https://github.com/rust-lang/rust/pull/76172). Constify the following methods of `core::cmp::Ordering`: - `reverse` - `then` Insta-stabilizes these methods as const under the `const_ordering` feature, as their implementation is a trivial match and the recent stabilization of #49146 (Allow `if` and `match` in constants). Note: the `const_ordering` feature has never actually been used as these methods have not been `#[rustc_const_unstable]`. Tracking issue: #76113