If a & simple selector is on a style rule with no parent style rule,
then it behaves like :scope - but notably, :scope provides 1
specificity in the class category, but & is supposed to provide 0.
To solve this, we stop replacing it directly, and just handle the & like
any other simple selector. We know that if the selector engine ever
sees one, it's equivalent to :scope, because the nested ones will have
been replaced with :is() before that point.
This gets us one more subtest pass. :^)
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.
