Issue Description:

First time post, so kindly let me know if I'm going against any guidelines.

The below code prompts an error in Xcode with quick-fix stating:

Argument of '#selector' refers to instance method 'btnHandler(sender: ))' that is not exposed to Objective-C``Add '@objc' to expose this instance method to Objective-C

However, applying the quick-fix adds `@objc` to the btnHandler line in the protocol definition instead of the instance method.

import UIKit

protocol SomeProtocol {
    func setupButton()
    func btnHandler(sender: UIBarButtonItem)
}

extension SomeProtocol {

    func setupButton() {
        let button = UIBarButtonItem()
        button.action = #selector(btnHandler)
    }

    func btnHandler(sender: UIBarButtonItem) { }
}

I know that @objc can't be used in non-concrete extension, however the syntax auto-correct behavior seems odd.

edit: fixed mistake in example, pointed out by @theblixguy