[ReturnSelf] Allows Protocols to Return Self

[tinder-maxwellelliott]

Currently Mockolo is broken for Protocols that return Self. These changes ensure that we return the mock class type when we encounter a Self return type:

Example protocol that breaks Mockolo currently

/// @mockable
protocol NonSimpleFuncs {
    @discardableResult
    func returnSelf() -> Self
}

[elsh]

thanks for the change