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/incubator.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <qobject.h>
+#include <qpointer.h>
 #include <qqmlincubator.h>
 #include <qtmetamacros.h>
 
@@ -25,7 +26,37 @@ signals:
 	void failed();
 };
 
-class DelayedQmlIncubationController: public QQmlIncubationController {
-	// Do nothing.
-	// This ensures lazy loaders don't start blocking before onReload creates windows.
+class QSGRenderLoop;
+
+class QsIncubationController
+    : public QObject
+    , public QQmlIncubationController {
+	Q_OBJECT
+
+public:
+	void initLoop();
+	void setIncubationMode(bool render);
+	void incubateLater();
+
+protected:
+	void timerEvent(QTimerEvent* event) override;
+
+public slots:
+	void incubate();
+	void animationStopped();
+	void updateIncubationTime();
+
+protected:
+	void incubatingObjectCountChanged(int count) override;
+
+private:
+// QPointer did not work with forward declarations prior to 6.7
+#if QT_VERSION >= QT_VERSION_CHECK(6, 7, 0)
+	QPointer<QSGRenderLoop> renderLoop = nullptr;
+#else
+	QSGRenderLoop* renderLoop = nullptr;
+#endif
+	int incubationTime = 0;
+	int timerId = 0;
+	bool followRenderloop = false;
 };