audio: Another attempt to make device add/remove work vs event watchers.

This patch reverts the previous reversion, and then adds code to queue up
events to be sent the next time SDL pumps the event queue. This guarantees
that the event watcher/filter _never_ runs from an SDL audio device thread
or some other backend-specific internal thread.

src/audio/emscripten/SDL_emscriptenaudio.c

@@ -181,8 +181,6 @@ static int EMSCRIPTENAUDIO_OpenDevice(SDL_AudioDevice *device)
         return SDL_OutOfMemory();
     }
 
-    RefPhysicalAudioDevice(device);  // CloseDevice will always unref this through SDL_AudioThreadFinalize, even if we failed to start the thread.
-
     // limit to native freq
     device->spec.freq = EM_ASM_INT({ return Module['SDL3'].audioContext.sampleRate; });