doc: unify format of iterables

[vsemozhetbyt]

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• documentation is changed or added
• commit message follows commit guidelines

Also, make signatures easier for copy-paste testing.

[vsemozhetbyt]

CI-lite: https://ci.nodejs.org/job/node-test-pull-request-lite/521/

[TimothyGu]

I personally feel @@ is nicer to read, and especially compact in tables of contents. But I won't block this.

[vsemozhetbyt]

@TimothyGu I mean mostly these reasons:

• Code examples do not contain low-level fragments to copy-paste and test things like iterator.next(), so it can be handy to have JS code in signatures.
• @ symbols just in these two headings make general doctools parsing RegExps more complicated.

However, if somebody does have objections, I will revert these parts.

[vsemozhetbyt]

Landed in ff4ca64

[TimothyGu]

@vsemozhetbyt

• Code examples do not contain low-level fragments to copy-paste and test things like iterator.next(), so it can be handy to have JS code in signatures.

Interesting point. On the other hand, it inspires the question of who would want to copy-paste this function in the first place since it's such a low level API.

• @ symbols just in these two headings make general doctools parsing RegExps more complicated.

Fair point, but I'm not convinced that should be the primary reason this gets landed.

---

Procedurally, I am not very happy with how this PR was fast-tracked. Even though I did not explicitly block this pull request, I'd like to note that COLLABORATOR_GUIDE says:

Before landing pull requests, sufficient time should be left for input from other Collaborators.

In the future I would prefer to get a chance to reply to any responses to my comments before the PR gets merged rather than after, especially considering the fact that this PR was created and applied in a 20-hour span over the weekends.

[vsemozhetbyt]

@TimothyGu Sorry. I will wait more time if any non-blocked concerns expressed.