This doesn't implement full sound support but stubs out most of the
sound code under SDL3, so that we can implement it piecemeal.
Implemented here:
1. Sound device initialization.
2. SVid sound playback.
Does not add a dependency on `SDL_mixer`: SDL3 built-ins
are enough to play SVid audio.
In C++, globals initialization order accross translation units is not
defined. Accessing a global via a function ensures that it is initialized.
This will be needed for #7638, which will statically initialize change
handlers after the Options object has been initialized.
Each resampler allocates an input buffer and an output buffer.
Since we create ~100 audio stream objects (1 per `sfx_MISC` effect),
the memory cost of these buffers adds up.
Avoids creating a resampler when the audio sampler rate matches the
output sample rate. This is mostly the case when the output sample
rate is 22050.
Gleb Mazovetskiy