Experiment using SDL3

[iboB]

Currently we use SDL2 for multimedia examples and tools. SDL3 gives us camera access and proper video playback. Unfortunately it's still alpha and there is not an official stable release. From a bit of research it's still quite usable, so it will likely work for us. Unfortunately we would have to build it (and add it to the repo in source or binary form) ourselves.

Low prio as there is no urgent need for it yet.