feat(windows-ble): auto-pair on characteristic read

[igiona]

I noticed that on Windows, when I try to read a pairing-protected characteristic the Windows implementation simply returns null.

In the mobile apps though, the OS detect such a read and automatically performs a pairing request and the user gets prompt with the standard pairing UI.
In my case I'm using justworks, hence a simple "yes/no" is prompted.

When I try to read that characteristic while unpaired on Windows, I get a ProtocolError status (I would guess that AccessDenied is more appropriate, but that's what I see..)

This PR as-is, is meant to trigger a discussion on this issue more than being real merge-request.

Attempt1 Basic Pairing

Here for me the pairing never worked, Service.Device.NativeDevice.DeviceInformation.Pairing.PairAsync() always immediately returned the status Failed.
I'll tried to debug further more this. Every suggestion is welcomed.

Attempt2 (this PR) Custom pairing

The code introduces the iOS & Android behaviour on Windows, although I did not implemented any UI hence the pairing happens silently and works only in a justworks scenario (not good of course, but I wanted to get it to work quick&dirty).

What's your opinion on this @peterfoot ?
Do you like to align the behaviour to the mobile platforms?

[peterfoot]

Sorry for the delay in responding. I like the idea of this, and I'm guessing it will need implementing on writes as well. I share your concern about how to handle other pairing types, I think the behaviour on mobile would be to prompt the user with the standard UI but I would need to test this. I think this functionality is very much needed as by following the WebBluetooth model there is no explicit pairing API and so it needs to be smarter like this.