fix(cli/js/net): Make generator return types iterable

[nayeemrmn]

Strengthens the type so this doesn't throw a type error:

const iterator = Deno.listen({ port: 10000 })[Symbol.asyncIterator]();
for await (const n of iterator);

i.e the iterators are also iterable.

[ry]

I don't really understand. Why would you want to do that?

[nayeemrmn]

That's how generators are defined everywhere else, this was a mistake. Generators provide this property but those type defs are hiding it. If it really needs a use case, I suppose there is a different behaviour for two loops sharing the same iterator object which might be useful to someone.

[bartlomieju]

That's how generators are defined everywhere else, this was a mistake. Generators provide this property but those type defs are hiding it. If it really needs a use case, I suppose there is a different behaviour for two loops sharing the same iterator object which might be useful to someone.

This type declaration confirms that:
https:/microsoft/TypeScript/blob/712967b2780e8ecd28f8f1e2e89c1ebd2592bb4c/lib/lib.es2018.asynciterable.d.ts#L32-L45

LGTM