[WebDriver BiDi] Respect user context

[sadym-chromium]

In WebDrive BiDi, there is a concept of user context, which is similar to CDP's BrowserContext, which, in turn, is similar to Chrome's incognito profile.

Should Bluetooth Simulation be a BrowserContext-specific, or it should be shared between all the BrowserContexts?

Related issue: #635

[reillyeon]

I'm not sure whether this is really separate from the other issue. In normal operation real Bluetooth devices are global to the whole system so from that perspective having simulated Bluetooth devices be specific to a particular tab or profile is a departure from normal behavior. On the other hand it's probably useful for test automation to not have the operations of one test interfering with another, which browser-wide simulated Bluetooth devices could do.

Implementation concerns however mean that it's hard to mix providing simulated and real Bluetooth devices to the same page and so we're probably stuck with having simulated devices more tightly scoped.