Flag redundant access levels same as enclosing context

[danwood]

It would be great to flag code that is marked with an explicit access level (internal, private, fileprivate) that is redundant to the access level of the type that is enclosing that code.

I have already implemented this on a private branch - I'm just waiting to deal with #1042 before presenting this.

Not determined : Should this have its own flag? Or to avoid having too many new flags, could this feature be folded into an existing flag?

Here are some example of code that should be flagged. (The inner declarations, not the outer, and not the "(set)" specifiers)

private class Private {
    private var x: Int
}

fileprivate class FilePrivate {
    fileprivate var data: String = ""
    fileprivate func method() {}

    fileprivate struct Config {
        fileprivate var value: Int = 0
    }
}

internal class Internal {
    internal var count: Int = 0
}

fileprivate class SetterExample {
    fileprivate fileprivate(set) var redundantSetter: Int = 0
    fileprivate private(set) var redundantAccess: Int = 0
}

internal class InternalSetterExample {
    internal internal(set) var redundantBoth: Int = 0
    fileprivate fileprivate(set) var redundantSetter: Int = 0
    internal private(set) var redundantAccess: Int = 0
}

private class PrivateSetterExample {
    private private(set) var redundantBoth: Int = 0
}