[RFC] Key-paths for methods vs. key-path literals with methods

Evolution Discussion
6

Because of SE-0249 we kinda made the function syntax that we wanted to abandon in SE-0042 relevant again.

// SE-0042 using key-path literals
\.hasPrefix as (String, String) -> Bool

// SE-0249 using key-path literals
\.hasPrefix as (String) -> ((String) -> Bool)