Tracking issue for `Result::map_or`

[tesuji]

PR #66292 added Result::map_or with implementation:

impl<T, E> Result<T, E> {
    pub fn map_or<U, F: FnOnce(T) -> U>(self, default: U, f: F) -> U {
        match self {
            Ok(t) => f(t),
            Err(_) => default,
        }
    }
}