Explicitly redirect/archive this repo

[gsnedders]

w3c/csswg-drafts#3433 merging this into CSSOM was resolved in 2021, so anyone referring to the WICG draft is looking in the wrong place. Except there's nothing in that draft to suggest it's the wrong place, and searching for constructible stylesheets leads here more quickly than CSSOM.

[tabatkins]

I don't have admin permissions to this repo to actually retire it, but I've changed the README to link to CSSOM now. @marcoscaceres ?

[gsnedders]

https://wicg.github.io/construct-stylesheets/ should be explicit in being retired, too.

[marcoscaceres]

CC'ing @WICG/chairs (I no longer have permissions either, sorry @tabatkins)

[yoavweiss]

@tabatkins Can you send a PR redirecting the spec link to where it was integrated into CSS?

Otherwise, there are 28 open issues and 3 PRs. Should we close them before archiving?

[annevk]

I think they should be triaged. I'd really like to know if they either have follow-up issues or are actually resolved.