The AbstractBackend registers itself in the WaylandServer allowing
external users to easily get to the backend and not needing to test
manually which backend is used.
WaylandServer allows to create a ClientConnection which is intended for
QtWayland. This allows us to easily identify our "own" surfaces. The
created file descriptor is set as env variable WAYLAND_SOCKET prior to
creating the Application. Wayland will unset it after connecting, so we
don't need to unset it. This removes the hack of setting and resetting
the WAYLAND_DISPLAY environment variable.
Creates a socketpair in WaylandServer and creates a ClientConnection for
Xwayland. The created file descriptor is passed to Xwayland through the
WAYLAND_SOCKET env variable.
The WaylandServer is at the moment only used to support starting an
Xwayland. It does not support Wayland clients yet, so don't get
excited.
For Xwayland it's using the trick of creating the Display before the
QApplication is created with manual event dispatching.
