Migrate to SDL3 and SDL Render or GPU

[MaddTheSane]

As some platforms don't have a native OpenGL renderer, perhaps migrating to a more agnostic API like SDL Render or SDL_GPU. This mainly affects Windows on ARM and iOS, but macOS will probably have better performance if a more recent rendering API is targeted.

[fgenesis]

I'm planning to do this eventually, but it'll take a while to get there. I've slowly exchanged most glImmediate uses to VBOs as a first step, but ideally "BBGE" should be split up into "the engine" producing work for "the renderer", decoupled imgui-style.
Since this is a first for me and i'm not entirely sure how to tackle this in a way i won't regret later, do you have any useful material on this? Ideally not breaking backwards-compatibility to very old GL backends.
I was thinking something like a per-game-layer RenderList, that consists of (texture, matrix, blendmode, uv, ...).
Pro: There are ~70 independent layers so this could be done in parallel.
Con: Uses extra scratch memory per-frame for the render lists, esp. if a lot is visible on the screen.

Thoughts?