Qt3D support for double-precision floating point

I promised a client (using Qt3D for a detailed CAD type of application) I would log a bug. They went through a lot of problems because they operate in double precision, but have to convert to float for Qt3D (and the Qt classes that uses such as QVector3D).

I saw QTBUG-8211 (although that was for the pre-KDAB Qt3D), and I understand we still want to emphasize portability and speed. However, it should be noted there are use cases for double such as the super-detailed CAD use case where both visually and camera-control wise double is better. And OpenGL / Vulkan shaders and supposedly some hardware exists that can do double floats.