Changed main callback return values to an enumeration

Fixes https://github.com/libsdl-org/SDL/issues/10515

examples/audio/01-simple-playback/simple-playback.c

@@ -17,7 +17,7 @@ static SDL_AudioStream *stream = NULL;
 static int total_samples_generated = 0;
 
 /* This function runs once at startup. */
-int SDL_AppInit(void **appstate, int argc, char *argv[])
+SDL_AppResult SDL_AppInit(void **appstate, int argc, char *argv[])
 {
     SDL_AudioSpec spec;
 
@@ -51,7 +51,7 @@ int SDL_AppInit(void **appstate, int argc, char *argv[])
 }
 
 /* This function runs when a new event (mouse input, keypresses, etc) occurs. */
-int SDL_AppEvent(void *appstate, const SDL_Event *event)
+SDL_AppResult SDL_AppEvent(void *appstate, const SDL_Event *event)
 {
     if (event->type == SDL_EVENT_QUIT) {
         return SDL_APP_SUCCESS;  /* end the program, reporting success to the OS. */
@@ -60,7 +60,7 @@ int SDL_AppEvent(void *appstate, const SDL_Event *event)
 }
 
 /* This function runs once per frame, and is the heart of the program. */
-int SDL_AppIterate(void *appstate)
+SDL_AppResult SDL_AppIterate(void *appstate)
 {
     /* see if we need to feed the audio stream more data yet.
        We're being lazy here, but if there's less than half a second queued, generate more.