Include disconnectedConnectionStatus in NotConnectedException

[curioustechizen]

Currently on Android, when a connection failure happens, the NotConnectedException is thrown. However, this exception does not carry the underlying Gatt Status. See here.

This means clients have to rely on the StateDisconnected instead of examining the NotConnectedException to know the status. Would you consider including the Disconnected.Status as a parameter in NotConnectedException?

I could take a stab at a PR if this makes sense to you.

[curioustechizen]

To add a some context to the above, I have a case where the exception masks the underlying cause. Here's the scenario:

• We have a BLE peripheral that has a limit on the number of bonds it can store
• When that limit has been reached, trying to connect a new central to that peripheral fails
• On Android, this can be seen in onConnectionStateChanged with the status 5 (GATT_INSUFFICIENT_AUTHENTICATION)
• However, with Kable this is not surfaced in the NotConnectedException. Instead it is only surfaced in State.Disconnected.

That last point bears a bit of explanation. From the logs here's what I see happening

1. Android app calls peripheral.cconnect()
2. The connection does go through at the gatt level (onConnectionStateChanged gets called with GATT_SUCCESS)
3. Kable transitions the state to State.Connecting.Services
4. Service discovery is successful
5. My app also calls requestMtuso that is initiated at this point
6. I see an exception com.juul.kable.GattStatusException: OnMtuChanged(mtu=23, status=GATT_ERROR(133))

The underlying reason is GATT_INSUFFICIENT_AUTHENTICATION; the OnMtuChanged(mtu=23, status=GATT_ERROR(133)) is just a symptom.

My proposal is that any time Kable throws a NotConnectedException, it also includes the status code (if available). This way clients can view these errors as connection errors rather than a Disconnected state.