Move SwiftUI's Identifiable protocol and related types into the standard library

[jayton (Jens Ayton)]

@anandabits

I have been working with Kyle Macomber from the SwiftUI team on a more fleshed out proposal. We have decided to strip it down to a bare minimum.

Could you summarize these discussions? In particular, I’m interested in the removal of identifiedValue, which would seem to make it impossible to implement Collection.identified(by:) (which seems generally useful) in terms of this protocol. Will SwiftUI have an additional abstraction over Identifiable?