Xwayland: add DRM leasing support
I rebased !248 and updated it to the latest version of the protocol.
Things left to do:
- support for multiple DRM devices
Xwayland crashes when KWin starts in
pScreen->rootis null. I assume that the problem is that the connectors get offered at startup, as delaying the offer on the compositor side avoids the crash
- Xwayland also crashes when starting SteamVR
- drmModeGetConnector fails when the connector is withdrawn and offered again