Adds new Popup types to WebEngineView too

The context is the attached sample which creates 2 windows. One is QMainWindow with a QWebEngineView inside. The other is similar that a WebEngineView inside Window. But some inconsistencies exist:
1. The dropdown list (the <select> element) is clipped by QML Window, but not by QMainWindow
2. By right click, a context menu if brought up, which is also clipped by QML WIndow.

It should be the limitation that those objects are just Item's and will be clipped. So maybe that can be improved by introduce https://doc.qt.io/qt-6/qml-qtquick-controls-popup.html#popupType-prop to WebEngineView too.