Made event and temporary string memory thread-local and added SDL_FreeEventMemory()

Fixes https://github.com/libsdl-org/SDL/issues/10283

src/dynapi/SDL_dynapi.sym

@@ -123,6 +123,7 @@ SDL3_0.0.0 {
     SDL_FlushEvent;
     SDL_FlushEvents;
     SDL_FlushRenderer;
+    SDL_FreeEventMemory;
     SDL_GDKSuspendComplete;
     SDL_GL_CreateContext;
     SDL_GL_DestroyContext;