Add: BinaryInteger/negate()

[oscbyspro]

The result of BinaryInteger/negated() is often assigned to self so having a mutating convenience for it might be nice.

x.negate().discard() // with wrapping behavior
x.negate().unchecked("this can't fail because...")

extension BinaryInteger {

    /// Forms the additive inverse of `self` and an `error` indicator.
    @inlinable public mutating func negate() -> Fallible<Void> {
        let error: Bool
        (self, error) = self.negated().components()
        return Fallible(Void(), error: error)
    }
}

[oscbyspro]

I don't want too many mutating conveniences but I think negate() is in the same class as toggle(), mainly because a binary integer negate() is a fallible sign.toggle() in sign-and-magnitude algorithms.

[oscbyspro]

I also don't see much point in adding a Fallible/negate() because mutating is already an opt-out of the recovery chain.