[SDL3]Initial support with renderer software

[ilmich]

Hi @XProger , thanks for this wonderful project. With this pull request, I added initial support for the new SDL3 libraries. For now, it's possible to use only software rendering (which has some bugs, but I will send a dedicated pull request), but I will also integrate the OpenGL/GLES engine.

The main reason for this initial choice is that on some low-powered devices and with opensource software stack (mesa3d) the GLES engine does not work because the compiler is not optimized and generates shaders too large for the gpu (mali 400p2). Software rendering, on the other hand, works fine.

Greetings Michele