XWayland fixups
Little fixups to go hand-in-hand with X11-through-Xwayland enablement in QtMir.
- Enables the Xwayland and it's own wrapper in the systemd Lomiri wrapper
- Launches Xwayland (hybris or mainline) with EGL_PLATFORM=wayland
- Fixes placeholder windows staying around after killing an Xwayland window's process
Edited by Alfred Neumayer