view-transitions: Ensure correct style inheritance for pseudo DOM.

Add a test to ensure style inheritance is as expected in the tree of
pseudo-elements generated for a transition.

R=vmpstr@chromium.org

Change-Id: I70cedd4a168c4a61e4d84c404d32a64918855a14
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4000563


Reviewed-by: Vladimir Levin <vmpstr@chromium.org>
Auto-Submit: Khushal Sagar <khushalsagar@chromium.org>
Commit-Queue: Khushal Sagar <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1067726}