wayland: Simplify startup of compositor

At the moment, the wayland compositor has to handle the case of having
no workspace. This should be unnecessary and it creates a pesky cycling
dependency between Workspace and Compositor.

Given that the Workspace acts more like a container and kwin starts
accepting client connections after starting compositing, it's possible
to create the Workspace earlier and simplify the start() function a bit.

autotests/integration/kwin_wayland_test.cpp

@@ -146,6 +146,10 @@ void WaylandTestApplication::performStartup()
     createVirtualInputDevices();
 
     WaylandCompositor::create();
+    createWorkspace();
+    createColorManager();
+    createPlugins();
+
     connect(Compositor::self(), &Compositor::sceneCreated, this, &WaylandTestApplication::continueStartupWithScene);
 }
 
@@ -153,10 +157,6 @@ void WaylandTestApplication::continueStartupWithScene()
 {
     disconnect(Compositor::self(), &Compositor::sceneCreated, this, &WaylandTestApplication::continueStartupWithScene);
 
-    createWorkspace();
-    createColorManager();
-    createPlugins();
-
     waylandServer()->initWorkspace();
 
     if (!waylandServer()->start()) {

src/compositor_wayland.cpp

@@ -45,12 +45,7 @@ void WaylandCompositor::start()
         return;
     }
 
-    if (Workspace::self()) {
-        startupWithWorkspace();
-    } else {
-        connect(kwinApp(), &Application::workspaceCreated,
-                this, &WaylandCompositor::startupWithWorkspace);
-    }
+    startupWithWorkspace();
 }
 
 } // namespace KWin

src/main_wayland.cpp

@@ -145,6 +145,9 @@ void ApplicationWayland::performStartup()
     createTabletModeManager();
 
     WaylandCompositor::create();
+    createWorkspace();
+    createColorManager();
+    createPlugins();
 
     connect(Compositor::self(), &Compositor::sceneCreated, outputBackend(), &OutputBackend::sceneInitialized);
     connect(Compositor::self(), &Compositor::sceneCreated, this, &ApplicationWayland::continueStartupWithScene, Qt::SingleShotConnection);
@@ -153,10 +156,6 @@ void ApplicationWayland::performStartup()
 void ApplicationWayland::continueStartupWithScene()
 {
     // Note that we start accepting client connections after creating the Workspace.
-    createWorkspace();
-    createColorManager();
-    createPlugins();
-
     if (!waylandServer()->start()) {
         qFatal("Failed to initialze the Wayland server, exiting now");
     }