core: switch to custom incubation controller

This change requires more QtPrivate usage but eliminates generation or
cleanup related window incubation controller bugs. Additionally it
enables async loads prior to rendering windows.

src/core/generation.hpp

@@ -65,7 +65,7 @@ public:
 	QFileSystemWatcher* watcher = nullptr;
 	QVector<QString> deletedWatchedFiles;
 	QVector<QString> extraWatchedFiles;
-	DelayedQmlIncubationController delayedIncubationController;
+	QsIncubationController incubationController;
 	bool reloadComplete = false;
 	QuickshellGlobal* qsgInstance = nullptr;
 
@@ -89,7 +89,7 @@ private slots:
 
 private:
 	void postReload();
-	void assignIncubationController();
+	void updateIncubationMode();
 	QVector<QQuickWindow*> trackedWindows;
 	bool incubationControllersLocked = false;
 	QHash<const void*, EngineGenerationExt*> extensions;