Create "topic: shadow" label

[annevk]

Would it be possible to create a "topic: shadow" label to be able to track issues such as #1995 and others? If you're comfortable giving me edit access I'd be happy to help triaging.

That'd make it easier to track upstreamed work from w3c/components.

cc @tabatkins @TakayoshiKochi

[tabatkins]

I just bugged @astearns to give you edit access to the repo.

[plinss]

Access granted...

[annevk]

Excellent: topic: shadow . While looking around I found many issues that were not directly linked to the two CSS drafts focused on shadow tree selectors, so this seems to have been worth it.