Fully committing to it...!
This left SDL_wave.* alone for now, since there's a ton of comments in there
and this code hasn't changed much from SDL2 so far. But as SDL2 ages out a
little more, I'll likely switch this over, too.
I have no way to compile or test this atm, so this will likely need
further attention. I ended up cleaning this up a ton and adding missing
features, so the code changes are pretty dramatic vs a simple conversion
to SDL3...so tread carefully in here.
