Rule Request: Prefer if and switch expressions

[SimplyDanny]

In version 5.9, Swift got support for if and switch expressions. A rule to enforce them where allowed should be possible.

In the first implementation, the rule does not need to be configurable. It should be opt-in and might support automatic rewriting.

Triggering:

func f(cond: Bool) -> Int {
    if cond {
        return 1
    } else {
        return 2
    }
}

func f(cond: Bool) {
    let r: Int
    if cond {
        r = 1
    } else {
        r = 2
    }
}

Non-triggering:

func f(cond: Bool) -> Int {
    if cond {
        // Nothing
    } else {
        return 2
    }
    return 1
}