[SE-0258] Add implicit initialization via wrapper's init().
[SE-0258] Add implicit initialization via wrapper's init().

David Hart suggested this a while ago, and it makes a lot of
sense. Existing examples (like DelayedMutable and DelayedImmutable)
benefit, as do other future-looking ideas (e.g., replacing things like
@IBOutlet).

anandabits/swift-evolution,Nirma/swift-evolution,DevAndArtist/swift-evolution,abertelrud/swift-evolution,hartbit/swift-evolution,apple/swift-evolution,Nirma/swift-evolution,abertelrud/swift-evolution,DevAndArtist/swift-evolution,anandabits/swift-evolution,natecook1000/swift-evolution,ddunbar/swift-evolution,apple/swift-evolution,ddunbar/swift-evolution,natecook1000/swift-evolution,hartbit/swift-evolution