PropertyWrapper: AppStorage backport

AppStorage.swift

@propertyWrapper
struct AppStorage<Value>: DynamicProperty {
    let key: String
    let defaultValue: Value

    init(wrappedValue defaultValue: Value, _ key: String) {
        self.key = key
        self.defaultValue = defaultValue
        self._wrappedValue = State(wrappedValue: UserDefaults.standard.object(forKey: key) as? Value ?? defaultValue)
    }

    @State var wrappedValue: Value {
        didSet { UserDefaults.standard.set(wrappedValue, forKey: key) }
    }
    var projectedValue: Binding<Value> {
        return Binding(
            get: { wrappedValue },
            set: { wrappedValue = $0 }
        )
    }
}