Convert adafruit_bus_device, adafruit_pixelbuf, analogio, atexit, audiobusio, audiocore, audioio, audiomixer, and audiomp3 modules to use MP_REGISTER_MODULE.
Related to #5183.
When nrf pwm audio is introduced, it will be called `audiopwmio`. To
enable code sharing with the existing (dac-based) `audioio`, factor
the sample and mixer types to `audiocore`.
INCOMPATIBLE CHANGE: Now, `Mixer`, `RawSample` and `WaveFile` must
be imported from `audiocore`, not `audioio`.