The Wayland event queue is moved into a dedicated thread and a
new class is created for just creating the connection and listening
for events. The WaylandBackend creates the thread and uses an event
queue for the main thread.
REVIEW: 119761
KWin_Wayland still needs an X-Server. To simplify the development
setup the required X-Server can be started through a command line
argument together with KWin. Unfortunately the command line arguments
processing needs to be done by hand as QCommandLineParser only allows
processing after QApplication is created which requires the started
X Server.
The nested X-Server is started by forking the application and using
execlp to load the binary. In addition a pipe is created to allow the
X-Server to write the display number to once it's ready to connect and
by that KWin is ready to create the QApplication.
All of kwin except the main function goes into a new (private) library
called kwin. Two new kdeinit_executables are created:
* kwin_x11
* kwin_wayland
Both only use a dedicated main_x11.cpp and main_wayland.cpp with the
main function and a KWin::Application subclass and linking the new
kwin library.
The main idea behind this is to be able to perform more sane sanity
checks. E.g. on Wayland we don't need to first test whether we can
create an X11 connection. Instead we should abort if we cannot connect
to the Wayland display. Also the multi-head checks are not needed on
Wayland, etc. etc. As most of that code is in the main function to
simplify it's better to split.
This will also make it easier to diverge more easily in future. The
Wayland variant can introduce more suited command line arguments for
example. This already started by having the --replace option only
available in X11 variant. The Wayland backend is still a window manager,
but doesn't claim the manager selection.
