Add new classes and functions in Qt 6
There are lots of new classes and functions in Qt 6 that we can add bindings for. Thankfully Qt has what's been added listed out in their docs.
What's new in Qt 6.0: https://doc.qt.io/qt-6/whatsnew60.html#new-modules-in-qt-6-0
New classes and functions in Qt 6.0: https://doc.qt.io/qt-6/newclasses60.html
(Spun off from issue #51.)