css: Add fast-path for parent selector matching

css: Add fast-path for parent selector matching

Add a fast path for parent selector matching that uses a bloom filter to
quickly discard selectors that can't possibly match.

Keep in mind that we match using a bloom filter, so we might
accidentally include too many selectors when hash/bucket collisions
occur.
That's not a correctness problem though, because we'll do a real check
afterwards.

The idea for this change is taken from browsers, in particular WebKit.