Drop RtAudio driver on Windows

We've been defaulting to WASAPI since 3.0 and it's superior to RtAudio
in all aspects.

Obsoletes and closes #25503.

Also enable WINMIDI on MinGW, this had been missed initially.

Fix os_windows.cpp and crash_handler_windows.cpp which had weird
dependencies on RtAudio.h's includes (ugh).

platform/server/os_server.h

@@ -32,7 +32,6 @@
 #define OS_SERVER_H
 
 #include "drivers/dummy/texture_loader_dummy.h"
-#include "drivers/rtaudio/audio_driver_rtaudio.h"
 #include "drivers/unix/os_unix.h"
 #include "main/input_default.h"
 #ifdef __APPLE__