Fix exclusivity warnings in JSONEncoder
Fix exclusivity warnings in JSONEncoder

Bring in changes from the Swift overlays to avoid exclusivity warnings. These
changes come from: https://github.com/apple/swift/pull/10821

apple/swift-corelibs-foundation,alblue/swift-corelibs-foundation,JGiola/swift-corelibs-foundation,parkera/swift-corelibs-foundation,parkera/swift-corelibs-foundation,alblue/swift-corelibs-foundation,parkera/swift-corelibs-foundation,parkera/swift-corelibs-foundation,apple/swift-corelibs-foundation,alblue/swift-corelibs-foundation,alblue/swift-corelibs-foundation,e78l/swift-corelibs-foundation,JGiola/swift-corelibs-foundation,JGiola/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,alblue/swift-corelibs-foundation,e78l/swift-corelibs-foundation,parkera/swift-corelibs-foundation,e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation,e78l/swift-corelibs-foundation,JGiola/swift-corelibs-foundation,e78l/swift-corelibs-foundation,JGiola/swift-corelibs-foundation