For example, a few ref tests have a match like this:
```
<link rel="match"
href="/css/reference/ref-filled-green-100px-square-only.html">
```
Previously we'd interpret this as `http://css/reference/...` which made
the test runner sad.
Because of this we no longer have to handle ahem.css in a special way.
This should find:
- <link rel=stylesheet>
- CSS `@import`s
- Any resources linked from a stylesheet with `url()`
There's a good chance there are other resources we'll want to copy too,
but CSS was a big hole.
This change switches the Meta/import-wpt-test.py script to using the
standard html.parser module rather than BeautifulSoup.
Otherwise, without this change, when a contributor first tries to run
the script, if they don’t have BeautifulSoup installed, it will fail.
Note that this patch also includes an unrelated small change that
switches to using os.path.normpath — rather than Path.absolute() — to
“normalize” the destination names of the downloaded test files.
This change makes the Meta/import-wpt-test.py script handle URLs such as
https://wpt.live//WebCryptoAPI/generateKey/../util/helpers.js and paths
containing, e.g., wpt-import/WebCryptoAPI/generateKey/../util/helpers.js
(that is, URLs and paths with “..” parent-directory references in them).
Otherwise, without this change, when the import-wpt-test.py script tries
a URL like https://wpt.live//WebCryptoAPI/generateKey/../util/helpers.js
which contains a “..” parent-directory reference, the script fails with
a “urllib.error.HTTPError: HTTP Error 404: Not Found” error message.
