Investigate switching to CDP color-contrast check

The check in aXe has given us a decent share of problems over the years.

There's new work that provides a protocol support to check contrast: [DevTools: Report low-contrast issues via the Issues panel](https://docs.google.com/document/d/1MRn5HjfLiM8vM41nL34yKsQrbZwrjqN6FEFM6I1DtWo/edit) cc @OrKoN

To try it out.. Do devtools on devtools and run this:

```js
let Main = await import('./entrypoints/main/main.js');
await Main.MainImpl.sendOverProtocol('Audits.enable');
await Main.MainImpl.sendOverProtocol('Audits.checkContrast');
```

And then look at the issues panel in the first devtools.


(Side-note: I don't know how this relates [to the APCA algorithm](https://developer.chrome.com/blog/new-in-devtools-89/#apca) that's under experiments).

Running on wikipedia it flagged a bunch of icon fonts. (Not sure if it's possible to ignore those).
But before we adopt this technique we'll need to do some analysis to see where this implementation differs from aXe and where the bugs are.

But it's exciting because this thing is quite fast. and would likely speed up our median LR run by a second. and 95pctl by a few. :)