QQuickFontLoaderPrivate uses static objects, which is not cleaned up when destroying the QApplication

in my use case, i need to create QApplication objects after destroying older QApplication objects: only one instance exists at a time, but it can be destroyed and re-created. however QQuickFontLoaderPrivate::fonts is a static variable, which is not cleaned up when the QApplication is destroyed.

steps to reproduce:
1. create QApplication
2. create QQuickView with a scene, loading a font
3. destroy the QApplication
4. create a new QApplication
5. create QQuickView with a scene, loading a font