Issue Description:

When overriding a function that has an implicitly unwrapped optional parameter with a non-optional parameter, the fixit suggests adding ?, making the parameter optional.

I would expect this to offer adding !, along with ?, but I am not sure if this is classed as a bug, or an intentional change due to SE-0054.

Example code that produces the fixit:

class Foo {
    func bar(_ bar: String!) {}
}

class FooSubclass: Foo {
    override func bar(_ bar: String) {}
}

This produces the message: Cannot override instance method parameter of type 'String?' with non-optional type 'String', with an Insert '?' fix.

If this is classed as a bug I'd love to attempt to fix it)