Add SDL3

[Ghabry]

To not break too much stuff I suggest to do this in multiple steps:

1. Add SDL3 and keep SDL2 for now. They dont have any file conflicts so this is safe to do
2. Change the default in the Player to SDL3

• For now keep emscripten (canvas scale issues) and Android (crashes) on SDL2

3. When everything is ported remove SDL2 in another PR to buildscripts

[carstene1ns]

We need X11 and/or Wayland packages on Debian and *buntu CI builders:
https://wiki.libsdl.org/SDL3/README-linux#build-dependencies
Or patch it to use -DSDL_UNIX_CONSOLE_BUILD=ON in the yaml.

[Ghabry]

about the build failure on our system: I can either install the packages or pass -DSDL_X11_XSCRNSAVER=OFF -DSDL_X11_XTEST=OFF

XSCRNSAVER is for e.g. disabling screen locking and XTEST for UI automation. Both arent required.

What do you prefer?

[carstene1ns]

Well, if I interpret the output correctly we do not have sound yet anyway. So additional package for e.g. pulse is needed as well. But I also think both extensions are not strictly needed for the build.