Support for SDL_mixer 3.2.2

[ericyoondotcom]

The first official release of SDL3_Mixer was published 3 weeks ago. There have been a number of API changes since the commit bindbc-sdl is pinned to.

Would be great is bindbc-sdl could be upgraded to support the official version of SDL3 Mixer. If I have time in the next few weeks I might take a look if I can put up a PR.

Thanks!