Use of `content-visibility` CSS rules can lead to false colour contrast issues being reported

Expectation: All content on the page should have its colour contrast evaluated correctly

Actual: Content that is not yet rendered (because of `content-visibility` rules in CSS) can result in false colour contrast issues being reported

Motivation: I'd like to avoid the false positives and get back to my 100 score on Lighthouse :)

---

I'm not sure if a bug exists for this already (I searched for `content-visibility` but couldn't find anything), but there has been some discussion of it last year on Twitter, including a comment from @straker (apologies if this issue is already being tracked elsewhere):

* https://twitter.com/slightlylate/status/1338281294694735872
* https://twitter.com/sundress/status/1338294674516107265
* https://twitter.com/StevenKLambert/status/1338632222178332676

You can see an example on https://infrequently.org as mentioned by @slightlylate on Twitter - colour contrast issues are reported with some of the `` elements, but these have a sufficient ratio.

Chrome 88.0.4324.96

Lighthouse 6.4.0

Reproduce the reported contrast issues on infrequently.org using the stated Chrome 88 and Lighthouse 6.4.0 versions, then trace how content-visibility affects contrast evaluation. Done means content hidden by content-visibility no longer produces false colour-contrast violations while visible content is still evaluated.

Written by the indexing model from the issue text.