Unwrap promises

[jablko]

Reopen #41960

// even through a double promise.
(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.evaluate(() => Promise.resolve(document.body.innerHTML)).then(s => {
    console.log('body html has length', s.length);
  });
});

Before

page.evaluate() returned a Promise<Promise<string>> ❌

Error in puppeteer
Error: /home/travis/build/DefinitelyTyped/DefinitelyTyped/types/puppeteer/puppeteer-tests.ts:554:43
ERROR: 554:43  expect  TypeScript@next compile error: 
Property 'length' does not exist on type 'Promise<string>'.
ERROR: 626:10  expect  TypeScript@next compile error: 

After

It returns a Promise<string> ✔️

• Use a meaningful title for the pull request. Include the name of the package modified.
• Test the change in your own code. (Compile and run.)
• Add or edit tests to reflect the change. (Run with npm test.)
• Follow the advice from the readme.
• Avoid common mistakes.
• Run npm run lint package-name (or tsc if no tslint.json is present).

[typescript-bot]

@jablko Thank you for submitting this PR!

🔔 @marvinhagemeister @cdeutsch @ksm2 @SimonSchick @serbanghita @JasonKaz @davecardwell @angrykoala @karol-majewski - please review this PR in the next few days. Be sure to explicitly select Approve or Request Changes in the GitHub UI so I know what's going on.

If no reviewer appears after a week, a DefinitelyTyped maintainer will review the PR instead.

[typescript-bot]

After 5 days, no one has reviewed the PR 😞. A maintainer will be reviewing the PR in the next few days and will either merge it or request revisions. Thank you for your patience!

[typescript-bot]

I just published @types/[email protected] to npm.