[iov-types] Symbol private public keys

[ethanfrey]

Based on microsoft/TypeScript#202 (comment), use:

declare const InputConnectorIdentity: unique symbol

idiom instead of

declare const enum InputConnectorIdentity = {}

I don't understand the difference between them both, but the first seems to be the more recently agreed upon in the ts discussion...

microsoft/TypeScript#4895 (comment)

[will-iov]

I'm not sure how I feel about this. Definitely enum is not a very helpful way of describing what's being done here, but the unique symbol approach seems to muddy the waters between types and instances somehow. I liked the cleanliness of

type AddressString = Address & string;

vs

type AddressString = typeof Address & string;

It would be more verbose, but what about this?

declare const AddressSymbol: unique symbol;
type Address = typeof AddressSymbol;
export type AddressString = Address & string;

[ethanfrey]

I had the same thought you did. But then figured I would just follow others design.

Please do update this with the symbol and type distinction