c307e90daa
Make `cow_is_borrowed` methods const Constify the following methods of `alloc::borrow::Cow`: - `is_borrowed` - `is_owned` Analogous to the const methods `is_some` and `is_none` for Option, and `is_ok` and `is_err` for Result. These methods are still unstable under `cow_is_borrowed`. Possible because of #49146 (Allow if and match in constants). Tracking issue: #65143