core/lazyloader: add LazyLoader

Also fixes qml incubation in general, which was completely broken,
meaning the native qml Loader type should also work now.

src/core/incubator.hpp

@@ -0,0 +1,30 @@
+#pragma once
+
+#include <qloggingcategory.h>
+#include <qobject.h>
+#include <qqmlincubator.h>
+#include <qtmetamacros.h>
+
+Q_DECLARE_LOGGING_CATEGORY(logIncubator);
+
+class QsQmlIncubator
+    : public QObject
+    , public QQmlIncubator {
+	Q_OBJECT;
+
+public:
+	explicit QsQmlIncubator(QsQmlIncubator::IncubationMode mode, QObject* parent = nullptr)
+	    : QObject(parent)
+	    , QQmlIncubator(mode) {}
+
+	void statusChanged(QQmlIncubator::Status status) override;
+
+signals:
+	void completed();
+	void failed();
+};
+
+class DelayedQmlIncubationController: public QQmlIncubationController {
+	// Do nothing.
+	// This ensures lazy loaders don't start blocking before onReload creates windows.
+};