Incorrect rendering of added/removed transparent objects

Was: "When deleting/creating Scene3DViews dynamically, then it is possible that the rendering of objects inside the scene are not rendered correctly in terms of depth".

Actually, (as discussed below in the comments) the issue is the handling of transparent objects, the objects are drawn in an arbitrary sequence, and if transparent ones are rendered before the opaque, the z value of the pixel skips the opaque one (as hidden), and if both are written.

For QtDesignStudio this came up in there as QT3DS-3515 and was solved there with a two pass rendering approach (opaque then transparent in Z order), and in Qt6.2 as discussed in QTBUG-92894.

In the example, when it is started then some of the scenes are correct, when the torus goes to the back behind the ring, then it is not rendering the torus at all. However in some of the scene3dviews then the torus is still visible (typically #3 in the view shows this). When changing the number of views to be just 2 then suddendly the torus is always rendered at the front, going down to 1 and then 2 again makes it go to the back.