fs: add support for async iterators to `fs.writeFile`

[yagipy]

Fixes: https://github.com/nodejs/node/issues/38075

Checklist

• [ ] make -j4 test (UNIX), or vcbuild test (Windows) passes
• [x] tests and/or benchmarks are included
• [x] documentation is changed or added
• [x] commit message follows commit guidelines

[yagipy]

@Linkgoron I am currently working on the following response. Are the following mistakes feasible in testing? https://github.com/nodejs/node/pull/38525#discussion_r628760262

I added the following test based on this test, but I was not able to reproduce the mistake. 😓 (The current implementation will pass.)

{
  const filenameLargeBuffer = join(tmpdir.path, 'testLargeBuffer.txt');
  const largeBuffer = {
    expected: 'dogs running'.repeat(512 * 1024),
    *[Symbol.iterator]() {
      yield Buffer.from('dogs running'.repeat(512 * 1024), 'utf8');
    }
  };

  fs.writeFile(
    filenameLargeBuffer, largeBuffer, common.mustSucceed(() => {
      const data = fs.readFileSync(filenameLargeBuffer, 'utf-8');
      assert.strictEqual(largeBuffer.expected, data);
    })
  );
}

[Linkgoron]

@Linkgoron I am currently working on the following response. Are the following mistakes feasible in testing? #38525 (comment)

I added the following test based on this test, but I was not able to reproduce the mistake. 😓 (The current implementation will pass.)

{
  const filenameLargeBuffer = join(tmpdir.path, 'testLargeBuffer.txt');
  const largeBuffer = {
    expected: 'dogs running'.repeat(512 * 1024),
    *[Symbol.iterator]() {
      yield Buffer.from('dogs running'.repeat(512 * 1024), 'utf8');
    }
  };

  fs.writeFile(
    filenameLargeBuffer, largeBuffer, common.mustSucceed(() => {
      const data = fs.readFileSync(filenameLargeBuffer, 'utf-8');
      assert.strictEqual(largeBuffer.expected, data);
    })
  );
}

It's quite difficult to reproduce, and I'm not sure in which cases write actually stops in the middle.

[yagipy]

@Linkgoron Fixed an issue where chunks might be partially written, referring to https://github.com/nodejs/node/pull/38615.

[jasnell]

@ronag @mcollina ... would definitely appreciate you taking a look at this one.