[SE-0320] Rename CodingKeyConvertible (#1421)
[SE-0320] Rename CodingKeyConvertible (#1421)

The text contains two mentions of `CodingKeyConvertible` (probably the old name?) that should be `CodingKeyRepresentable` to be consistent.
natecook1000/swift-evolution,apple/swift-evolution,apple/swift-evolution,abertelrud/swift-evolution,abertelrud/swift-evolution,natecook1000/swift-evolution