Add support for order-independent transparency

The current transparency implementation results in some problems when trying to render semi-transparent surfaces with QtGraphs Surface3D.

Some of the issues can be seen in the following videos:
https://qtcompany-my.sharepoint.com/:v:/g/personal/sakaria_pouke_qt_io/EVVP_ys6PzpFux3npEDYLJIBIZut4v1uNp9HigShbpgYWA?e=Ytc6wr
https://qtcompany-my.sharepoint.com/:v:/g/personal/sakaria_pouke_qt_io/EfUlvBKe8j1Cnxm7J6D6yX8Bgh-HVObaMs737HKmgjjOyw?e=uCIevc

Some techniques for doing this can be found here: https://on-demand.gputechconf.com/gtc/2014/presentations/S4385-order-independent-transparency-opengl.pdf

And here's a vulkan implementation of one: https://github.com/nvpro-samples/vk_order_independent_transparency