Expose Iterable publicly

[nandin-borjigin]

Some of the existing operators return Iterable and some others also expect Iterable.
However, due to lack of public operators (like map) on Iterable, we now have to leverage ReadonlyArray in the middle, which can be omitted if internal/Iterable is made public.

declare const set1: HashSet<string>;
declare const set2: HashSet<string>;

const tagged: HashMap<"tag1" | "tag2", string> = pipe(
  HS.values(set1),
  RA.fromIterable,
  RA.map(v => ["tag1", v]),
  RA.appendAll(pipe(
      HS.values(set2),
      RA.fromIterable,
      RA.map(v => ["tag2", v])
  )),
  HM.fromIterable
);

// becomes
const tagged: HashMap<"tag1" | "tag2", string> = pipe(
  HS.values(set1),
  Iterable.map(v => ["tag1", v]),
  Iterable.concat(pipe(
    HS.values(set2),
    Iterable.map(v => ["tag2", v])
  )),
  HM.fromIterable
)