Make cbPeripheral getter public

[martin-maierhuber-AP]

Hey, thanks for the great push forward to a more modern BLE implementation!

I have an issue when using typealias for CBPeripheral, when using another modules function that require a CBPeripheral. The typealias then results in a conflict. The SwiftBluetooth.Peripheral has a property cbPeripheral but its getter is internal. For compatibility reasons, please make that getter public to retain compatibility with other libraries or modules.

Thanks,
Martin