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/input.spec.js

@@ -18,10 +18,10 @@ const path = require('path');
 
 module.exports.addTests = function({testRunner, expect}) {
   const {describe, xdescribe, fdescribe} = testRunner;
-  const {it, fit, xit} = testRunner;
+  const {it, fit, xit, it_fails_ffox} = testRunner;
   const {beforeAll, beforeEach, afterAll, afterEach} = testRunner;
   describe('input', function() {
-    it('should upload the file', async({page, server}) => {
+    it_fails_ffox('should upload the file', async({page, server}) => {
       await page.goto(server.PREFIX + '/input/fileupload.html');
       const filePath = path.relative(process.cwd(), __dirname + '/assets/file-to-upload.txt');
       const input = await page.$('input');
@@ -34,7 +34,7 @@ module.exports.addTests = function({testRunner, expect}) {
         return promise.then(() => reader.result);
       }, input)).toBe('contents of the file');
     });
-    it('keyboard.modifiers()', async({page, server}) => {
+    it_fails_ffox('keyboard.modifiers()', async({page, server}) => {
       const keyboard = page.keyboard;
       expect(keyboard._modifiers).toBe(0);
       await keyboard.down('Shift');