Desktop - Bluetooth connection multiplexer
Summary
Adds the bluetooth connection multiplexer. This means that all transfers go over a single bluetooth connection, making them work reliably.
There are still lots of issues left with bluetooth, but this is a big step forward to me.
Test Plan
Enable the bluetooth backend in cmake -DBLUETOOTH_ENABLED=ON
and make sure your devices are paired. Connecting is quite slow initially, but should work within a minute. I only managed to get pc -> phone connecting to work, but I think that's unrelated to this work.
If you have trouble, try my bluetooth-extra
branch and manually fill in your device's bluetooth MAC.