feat: first argument to writable could be optional

[hunnble]

finish feature request at #6291
Only implement optional first argument for writable. It's unnecessary and inappropriate for readable.

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[ignatiusmb]

It's unnecessary and inappropriate for readable

How and why is it "inappropriate"?

Have you tried to check existing PRs before opening a new one? I suppose you do because this seems really similar to the PR exactly one number below. Why not help review the earlier PR and give your opinions why you deem it "unnecessary and inappropriate"?

[hunnble]

It's unnecessary and inappropriate for readable

How and why is it "inappropriate"?

Have you tried to check existing PRs before opening a new one? I suppose you do because this seems really similar to the PR exactly one number below. Why not help review the earlier PR and give your opinions why you deem it "unnecessary and inappropriate"?

The second argument of readable API(start/stop notifier) is required.I notice you made both first and second arguments optional, could you give a example when should we call readable() without these two arguments?

The first argument is allowed empty already(readable(undefined, startFn)).I saw issue #6291 and made a simple TS update for writable API, then i realized you've made it too...still not sure it's necessary to change readable API.

[dummdidumm]

This was fixed in #6293 , thank you for your contribution!