BTLE peripheral (server) API to report per-connection information

The QLowEnergyController on the peripheral (aka server) is able to serve multiple concurrent remote device connections at least on some platforms.

The current QLowEnergyController API could be amended with the ability to report certain information on a connection basis: each current connection have their own MTU, remote address and name, as well as connectivity status.

Notably this does not concern the "control" side of the QLowEnergyController as it can only ever be connected to a single device.