We already try to reconnect to our known devices when bluez5 appears on the bus or when the (pipewire) session gets started, so let's also do that as soon as the bluetooth adapter gets powered on.
Marked as RFC because I don't know if it was a deliberate decision to not do so. I think this would have the side effect of leaking all the connected devices and their MAC addresses to the public, for example iOS does not seem to do that kind of auto-connecting.