Initial optional SDL3 support

[Novum]

Currently just available with meson on Linux

[Novum]

Still some issues with fullscreen and performance is worse. Need to investigate. But since this is disable by default I think this is good to merge.

Edit: Was spinning on the task threads instead of properly waiting. It's fixed.

[j4reporting]

diff --git a/Quake/main_sdl.c b/Quake/main_sdl.c
index 426abb3..6dc5828 100644
--- a/Quake/main_sdl.c
+++ b/Quake/main_sdl.c
@@ -58,7 +58,11 @@ static void Sys_InitSDL (void)
        }
 
 #ifdef _DEBUG
+#ifdef USE_SDL3
+       SDL_SetLogPriorities (SDL_LOG_PRIORITY_DEBUG);
+#else
        SDL_LogSetAllPriority (SDL_LOG_PRIORITY_DEBUG);
+#endif
 #endif
 
        atexit (Sys_AtExit);