audio: Split Deinitialize into two stages.

First stage happens before we destroy objects, and is generally used to
shut down hotplug. The second stage is the usual deinit, which cleans up
the lowlevel API, unloads shared libraries, etc.

src/audio/wasapi/SDL_wasapi.h

@@ -58,6 +58,7 @@ int WASAPI_ProxyToManagementThread(ManagementThreadTask task, void *userdata, in
 // UNLESS OTHERWISE NOTED THESE ALL HAPPEN ON THE MANAGEMENT THREAD.
 int WASAPI_PlatformInit(void);
 void WASAPI_PlatformDeinit(void);
+void WASAPI_PlatformDeinitializeStart(void);
 void WASAPI_EnumerateEndpoints(SDL_AudioDevice **default_output, SDL_AudioDevice **default_capture);
 int WASAPI_ActivateDevice(SDL_AudioDevice *device);
 void WASAPI_PlatformThreadInit(SDL_AudioDevice *device);  // this happens on the audio device thread, not the management thread.