Bluetooth api changes

[rickjansen-dev]

This would be the minimal changes I need to be able to integrate bluez support properly and avoid deadlocks.

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There's something else I'd like to propose, since the library targets .net standard 2.1 (and thus C# 8 is standard) maybe it's nice to leverage IAsyncEnumerable for the Discover method, so it becomes something like:

IAsyncEnumerable<PoweredUpBluetoothDeviceInfo> Discover(CancellationToken cancellationToken = default)

This way the newly discovered devices would be streamed to whoever is invoking the discovery as they become available.

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And about the BluetoothAdapter class, is this meant to be a representation of an actual bluetooth adapter, or is it more like an bluetooth managing class? Since at least on linux (and I assume on windows too), you can have multiple adapters and I guess it would be nice to have some interface to list and select the adapter you want (and provide some convenience methods to simply select the first one available)

Closes #117

[tthiery]

It is abstracting the adapter. I do not know how WinRT or WebBluetooth behave, whether they combine them or not. I mean the API is not exactly starting in both cases with an adapter enumeration. Will figure out.

Review and test this later

[tthiery]

Feedback on the merge request

• I tested most examples and they work beautifully on WinRT. So we are good here.
• When you add commits please always add in the last line a reference to an issue and a statement whether it is a breaking change (e.g. "Extend Discover Callback to be truly async #117 non-breaking").
• I do not consider this a breaking change, because this is not a contracted API surface.
• One example is broken (for other reasons) which i will fix on opportunity.