WIP: Initial Bluetooth handoff impl

[Wazzaps]

This is an initial implementation of my new KDE connect feature:

It lets you move bluetooth devices between the PC and the phone. Mostly intended for wireless headphones.

TODO list:

• Add spinner while operation in progress
• Refine UX
• Try many more devices
  • Bluetooth LE devices probably won't work at all, though they might not need to (need to check if they have multipath by default)
• Make sure everything is translatable
• Un-uglify code (I don't know enough about GObjects to use it correctly)
  • There are numerous object lifetime problems (Why is this a problem in a GC'd language? Whatever), which cause soft-crashes of the extension.
    Example: Attempting to run a JS callback during garbage collection. This is most likely caused by destroying a Clutter actor or GTK widget with ::destroy signal connected, or using the destroy(), dispose(), or remove() vfuncs. Because it would crash the application, it has been blocked.
• BSD support (Decouple from bluez + find hardware with working bluetooth and bsd at the same time)
• Tests

[rohmishra]

For BT LE, Multi-Stream and Broadcast is for source. AFAIK receiving from multiple sources is still vendor dependent and not required.

[github-actions]

This pull request has conflicts, please resolve those so that the changes can be evaluated.