Auto merge of #11624 - g-k:wpt-cookie-path-tests, r=jdm

wpt cookie path tests

Adds wpt tests for the cookie path attribute.

Notes:

* I included polyfills for fetch and promise to get tests running.  Assuming these changes are OK, I'll remove them and add failure expectations so they don't get synced to w3c.
* I didn't work out a way to test sending cookies when the request and cookie paths exactly match (e.g. request path `/cookies/path/match-exact-page.sub.html` and cookie path `/cookies/path/match-exact-page.sub.html` will not send cookies to `/cookies/resources/echo-json.py`)
* test names could be clearer
* everything can be squashed to one commit

---

- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #8756 (github issue number if applicable).

- [x] These changes do not require tests because they are tests (and if we test our tests do we need to test our test tests? ...)

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