SlimeVR backend

[funnbot]

• Create IVRDriver interface that tracker/VRDriver.hpp can be derived from
• Create SlimeVRDriver that implements IVRDriver
• add https://github.com/SlimeVR/SolarXR-Protocol as a submodule
• use the generated cpp to implement the https://github.com/SlimeVR/SolarXR-Protocol/tree/main/schema/data_feed protocol.
• Wait for SlimeVR-Server to actually implement the solarxr protocol.
• Use boost.asio (or a smaller udp library, if its on vcpkg) for io.
• Add a way to switch IVRDriver implementations in the GUI