Provide migration path to UA Client Hints

[natevw]

At least some browser vendors intend to freeze the classic user agent string "soon":

• https://groups.google.com/a/chromium.org/g/blink-dev/c/-2JIRNMWJ7s/m/yHe4tQNLCgAJ (covered at https://css-tricks.com/freezing-user-agent-strings/ and https://medium.com/naver-fe-platform/prepare-for-client-hints-freezing-user-agent-9c0ea1ddd02c)
• https://web.dev/user-agent-client-hints/#introducing-the-new-user-agent-client-hints
• https://docs.microsoft.com/en-us/microsoft-edge/web-platform/user-agent-guidance#user-agent-client-hints
• https://developer.mozilla.org/en-US/docs/Web/API/Navigator/userAgentData
• https://wicg.github.io/ua-client-hints/#create-ua-list-section / https://wicg.github.io/ua-client-hints/#http-ua-hints

It is to be replaced by something a lot closer to what this library intends to do, but with some key differences:

1. it's based on an array of "brands" that ± always also includes a garbage value
2. platform/browser/etc. values normalize differently (e.g. macOS instead of Macintosh, Google Chrome and Chromium instead of Chrome…)

Ideally we could help match browsers all the way from the first implementations of JS to this new future.

[natevw]

As far as the normalization, it's probably best to roll with the likely platform brand names under the new spec and see what the major browsers as far as their own brand names.

Then what do we do with this idea of a list of browser brands rather than the single one we currently attempt?

1. Should we also return an array?
2. What does this mean for matching?
3. [Also, will this list give us useful insight on Safari-only platforms? Is Apple even on board with this spec at all?]

[natevw]

• https://caniuse.com/mdn-api_navigator_useragentdata (no Safari or Firefox at present!)
• https://chromestatus.com/feature/6311349754789888 / https://chromestatus.com/feature/5733498725859328
• https://mozilla.github.io/standards-positions/#ua-client-hints
• nada at https://webkit.org/status/

[natevw]

Given a list like:

1. Google Chrome
2. ))); DROP TABLE "not a brand"
3. Chromium

How should e.g. all: [Chromium, not: Chrome] behave? It seems like:

• $not must be true of every item in the list
• $any and $all may be true only of some item in the list

but I'm struggling to put this in terms of https://en.wikipedia.org/wiki/De_Morgan's_laws or whatever :-)

UPDATE: well there's something, sortof