Modernize the Qt graphics stack

Qt currently has several independent graphics stacks that serve different purposes. In some cases, it can be difficult or inefficient to combine output from the different stacks. Both for scalability and usability, we need to find a good way to unify the different stacks at different levels and make sure they work together as efficiently as possible.

The fragmentation in the stacks is also reflected in our tools. The ambition should be to have a unified experience of creating Qt applications, whether the content is 2D or 3D.

In addition, OpenGL is no longer the catch-all graphics protocol, so we need to open up and become more agnostic in this area.