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_winrt.cpp

@@ -220,7 +220,7 @@ int WASAPI_PlatformInit(void)
     return 0;
 }
 
-void WASAPI_PlatformDeinit(void)
+static void StopWasapiHotplug(void)
 {
     delete playback_device_event_handler;
     playback_device_event_handler = nullptr;
@@ -228,6 +228,17 @@ void WASAPI_PlatformDeinit(void)
     capture_device_event_handler = nullptr;
 }
 
+void WASAPI_PlatformDeinit(void)
+{
+    StopWasapiHotplug();
+}
+
+void WASAPI_PlatformDeinitializeStart(void)
+{
+    StopWasapiHotplug();
+}
+
+
 void WASAPI_EnumerateEndpoints(SDL_AudioDevice **default_output, SDL_AudioDevice **default_capture)
 {
     Platform::String ^ defdevid;