[Discussion] Inclusion of CasePaths into the language

Evolution Discussion
14

And beyond property access, it also enables other meaningful abstractions like PartialCasePath and a theoretical CasePathIterable protocol.

This ties in as a solution to the original Enum Quality of Life Improvements problem:

enum Navigation: CasePathIterable, Hashable {
    case firstScreen(FirstScreenData)
    case secondScreen(SecondScreenData)

    // Compiler generated
    static var allCasePaths: [PartialCasePath<Navigation>]
}

let navigationStep = Navigation.firstScreen([...])

// representing a case label
let unassociatedNavigationStep = \Navigation.secondScreen as PartialCasePath

// matching cases by label only
let isFirstScreen = navigationStep ~= \.firstScreen // true
let isSecondScreen = unassociatedNavigationStep == \.secondScreen // true

// counting total enum cases
let totalNavigationSteps = Navigation.allCasePaths.count // currently impossible to determine without hardcoding or dropping associated values
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