When we first parse a nested CSSStyleRule's selectors, we treat them as
relative selectors and then patch them up with an `&` as needed.
However, we weren't doing this when assigning the `cssText` attribute.
So, let's do that!
This gives us a couple of subtest passes. :^)
A few are skipped for now:
- A few ref tests fail
- Crash tests are not supported by our runner and time out
- top-level-is-scope.html crashes and needs further investigation
If a rule gets its caches cleared because it's moved in the OM, then its
child rules' caches are likely invalid and need clearing too.
Assuming that caches only point "upwards", this will correctly clear
them all. For the time being that will be true.
