Add Bluetooth.getDevices

[hamishwillee]

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This adds documentation for the new Bluetooth.getDevices() which was recently added to chromium (build 85) under a flag. Some docs on this here:

• https://docs.google.com/document/d/1RF4D-60cQJWR1LoQeLBxxigrxJwYS8nLOE0qWmBF1eo/edit
• https://googlechrome.github.io/samples/web-bluetooth/get-devices.html
• https://www.chromestatus.com/feature/4797798639730688

I tested this for Chrome, Edge, Opera for desktop on Windows. I rolled out to equivalent versions for some of the others. There are a couple of questions inline too.

FYI, this is one of the missing entries listed in #7585

PS When this is done will need to add compatibility table to https://developer.mozilla.org/en-US/docs/Web/API/Bluetooth/getDevices

[hamishwillee]

Thanks @ddbeck , I think this addresses your comments now

[ddbeck]

Looks great. Thank you! 🎉