Opacity for images/depth-images/videos/etc. is broken in 3D

[Wumpf]

The opacity feature on the re_renderer textured rectangle predates our new ability to sort drawables which got introduced in

• Add the ability to sort Drawables (new subdivision of DrawData) to re_renderer #11131

( this is not a regression of #11131, but it affects the behavior of this bug a bit)

Currently images draw always as part of the opaque phase, even when they're transparent. We have to put them in the right phase and correctly handle draw order

-> This is strongly related to

• Treat camera projected primitives in 3D space more like 2D objects #1025