[Xwayland-21.1] Backport fixes

Merged Olivier Fourdan requested to merge ofourdan/xserver:xwayland-21.1-backports into xwayland-21.1

This backports a couple of fixes for Xwayland 21.1.

Most importantly, this backports !751 (merged) which is required with NVIDIA proprietary driver Version 495.

CC: @cubanismo @jadahl @daenzer

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