Improve logging performance and make log priorities thread-safe

Fixes https://github.com/libsdl-org/SDL/issues/9679

test/testmanymouse.c

@@ -499,9 +499,6 @@ int main(int argc, char *argv[])
 {
     int i;
 
-    /* Enable standard application logging */
-    SDL_SetLogPriority(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_INFO);
-
     /* Log all events, including mouse motion */
     SDL_SetHint(SDL_HINT_EVENT_LOGGING, "2");