[nesting] Improve WPT coverage for top-level '&' specificity
The '&' selector, when it has no parent selector to draw from,
has a specificity of zero [1].
Blink already does the right thing. This CL just adds a new WPT
to enforce that behavior, and adjusts an existing tests which
expected specificity to be added.
Bug: 343794754
Change-Id: I3bfdba8a5db66be2d2cdd6f1b2f41b86aadbab9b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5982912
Reviewed-by: Steinar H Gunderson sesse@chromium.org
Commit-Queue: Anders Hartvoll Ruud andruud@chromium.org
Cr-Commit-Position: refs/heads/main@{#1376861}