Quick needs a way to set a default surface format for all QQuickWindows

There is currently no way to set a surface format on a Window from QML. This means that it is not possible to request a given OpenGL version and profile for windows that are created from QML. (unless one resorts to doing this in C++ before the windows gets visible)

See discussion in https://codereview.qt-project.org/#change,81097

The easiest solution is to add a static setter to QQuickWindow that sets a QSurfaceFormat which is then used in all QQuickWindow instances.

This still needs some additional solution to expose the version and profile to QML.