[GTK][WAYLAND] Create WaylandCompositorDisplay unconditionally when initializing...

[GTK][WAYLAND] Create WaylandCompositorDisplay unconditionally when initializing the WebProcess
https://bugs.webkit.org/show_bug.cgi?id=173598

Reviewed by Carlos Garcia Campos.

Move WaylandCompositorDisplay code to its own files so it can be used from other classes. Then, instead of
storing the waylandCompositorDisplayName in the WebProcess, keep a WaylandCompositorDisplay instance that
is created during the initialization. This way the appropriate sharedDisplayForCompositing will be set
since the creation of the WebProcess.

* PlatformGTK.cmake:
* WebProcess/WebPage/gtk/AcceleratedSurfaceWayland.cpp:
(WebKit::AcceleratedSurfaceWayland::create):
(WebKit::AcceleratedSurfaceWayland::AcceleratedSurfaceWayland):
* WebProcess/WebProcess.cpp:
(WebKit::WebProcess::initializeWebProcess):
* WebProcess/WebProcess.h:
(WebKit::WebProcess::waylandCompositorDisplay):
* WebProcess/gtk/WaylandCompositorDisplay.cpp: Added.
(WebKit::WaylandCompositorDisplay::create):
(WebKit::WaylandCompositorDisplay::bindSurfaceToPage):
(WebKit::WaylandCompositorDisplay::WaylandCompositorDisplay):
(WebKit::WaylandCompositorDisplay::registryGlobal):
* WebProcess/gtk/WaylandCompositorDisplay.h: Added.
* WebProcess/soup/WebProcessSoup.cpp:
(WebKit::WebProcess::platformInitializeWebProcess):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@218629 268f45cc-cd09-0410-ab3c-d52691b4dbfc