mmdevapi: Add a SW synth MIDI device.
This is an alternative approach to !7233: instead of creating an actual driver, just add a SW synth device in mmdevapi.
Other differences from !7233:
- Get rid of
struct swmidiand put everything in global variables. - Use static initialization for
cs, removeswmidi_init()andswmidi_exit().
Whole series for reference: https://gitlab.winehq.org/baskanov/wine/-/tree/mmdevapi-swmidi?ref_type=heads