Golang slices: add Reduce function

I propose a small, trivial addition to the slices package.

func Reduce[S ~[]E, E any, T any](s S, f func(T, E) T, init T) T {
    for _, v := range s {
        init = f(init, v)
    }
    return init
}

I often use similar func in other languages (js, PHP) and I think it'll be useful for GO as well.

I'm happy to contribute a PR with tests if this is a good idea.

Comment From: seankhliao

Duplicate of #61898