feat: experimental WebDriver BiDi support with Firefox

[OrKoN]

Previously, it was possible to use Firefox with Puppeteer relying on the Firefox's implementation of a subset of CDP. WebDriver BiDi is a new cross-browser automation protocol similar to CDP but unlike CDP it's a W3C standard meaning that it is well defined and easier to implement by the browser vendors.

This PR releases the option to turn on WebDriver BiDi when launching Firefox and use WebDriver BiDi instead of CDP to communicate with Firefox. The support level of the new protocol for Firefox is experimental and we are looking for your feedback!

The Puppeteer's WebDriver BiDi feature set for Firefox is almost the same as the previous CDP support. Few features that are still missing:

1. page.cookies and cookie management
2. puppeteer.connect
3. user agent emulation

We are constantly working on bringing new features and you can track the progress here and we hope to add support for remaining APIs and Chrome soon. Check out the WebDriver BiDi support to see if a particular API is supported with WebDriver BiDi.

Example of launching Firefox with WebDriver BiDi:

import puppeteer from 'puppeteer';

const browser = await puppeteer.launch({
  product: 'firefox',
  protocol: 'webDriverBiDi',
});
const page = await browser.newPage();
...
await browser.close();

[OrKoN]

@sadym-chromium @mathiasbynens PTAL. Any suggestions on the content for faq.md or any suggestions to document BiDi better?

[sadym-chromium]

@sadym-chromium @mathiasbynens PTAL. Any suggestions on the content for faq.md or any suggestions to document BiDi better?

Q: Does Puppeteer support WebDriver BiDi?

[sadym-chromium]

LGTM. We have quite good FF + BiDi support for announcing it as experimental.

[OrKoN]

After discussing with @jecfish and testing the website with these changes locally I think it might be better if we create a new page about WebDriver BiDi where we list what is supported and what is not. WDYT?

[jecfish]

Added a few comments on the docs. Otherwise, LGTM.