Fix crash in AlkWebPage::toHtml() on deleting the instance
From https://doc.qt.io/qt-5/qwebenginepage.html#toHtml When QWebEnginePage is deleted, the callback is triggered with an invalid value and it is not safe to use the corresponding QWebEnginePage or QWebEngineView instance inside it.
The variable on the stack for the event loop was affected in this specific case. Therefore, the corresponding variables are now generated dynamically.