build: port to meson

Meson has been gaining huge amounts of traction lately, especially in the Linux graphics community. It's much simpler and easier to reason about than cmake. Among the pool of likely contributors to Monado, the group with cmake literacy is shrinking and the group with meson literacy is growing.

This patch is 1:1 equivalent to the CMake build, but fixes some bugs with the build (such as various combiantions of drivers being enabled or issues with non-Linux systems) and leaves other existing bugs for solutions later (such as incomplete Windows support or issues selecting the various compositor drivers). I intend to fix at least compositor driver selection in a later patch, as I'll need to clean this up in order to work on DRM leasing via Wayland (which is mainly why I'm here).