Implement the drm-lease-v1 protocol

I'm currently looking at implementing DRM leasing in Mutter, and would appreciate it if Weston supported DRM leasing as a reference implementation. I have the kwin and wlroots implementations open right now to see how they do it, but both are more designed for their compositors (kwin being C++, and it's not too applicable to Mutter, and wlroots having some weird wlroots abstractions I can't apply here). As such, I'd appreciate it if a plain C reference implementation, with no (or little) additional abstractions, were available. Weston seems like the best place for that, especially as it is the reference Wayland compositor implementation.