chore(firefox): mark all Puppeteer tests that are failing on FF (#3924)

This patch:
- introduces new testRunner methods `addTestDSL` and `addSuiteDSL`
  to add annotated test / suite.
- introduces new test/suite declaration methods: `it_fails_ffox` and
  `describe_fails_ffox`. These are equal to `it`/`describe` for chromium
  tests and to `xit`/`xdescribe` for firefox.
- marks all unsupported tests with `it_fails_ffox`
- adds a new command-line flag `'--firefox-status'` to `//test/test.js`.
  This flag dumps current amount of tests that are intentionally skipped
  for Firefox.

End goal: get rid of all `it_fails_ffox` and `describe_fails_ffox`
tests.

Drive-By: remove cookie tests  "afterEach" hook that was removing
cookies - it's not needed any more since every test is run in a
designated browser context.

References #3889

test/worker.spec.js

@@ -2,11 +2,11 @@ const utils = require('./utils');
 const {waitEvent} = utils;
 
 module.exports.addTests = function({testRunner, expect}) {
-  const {describe, xdescribe, fdescribe} = testRunner;
+  const {describe, xdescribe, fdescribe, describe_fails_ffox} = testRunner;
   const {it, fit, xit} = testRunner;
   const {beforeAll, beforeEach, afterAll, afterEach} = testRunner;
 
-  describe('Workers', function() {
+  describe_fails_ffox('Workers', function() {
     it('Page.workers', async function({page, server}) {
       await Promise.all([
         new Promise(x => page.once('workercreated', x)),