dynapi: SDL_DYNAPI_entry must be in version script

For SDL dynapi to work, the SDL_DYNAPI_entry symbol must be externally visible.
Adding __attribute__((visibility(default))) would not work
since version scripts override these.

src/dynapi/SDL_dynapi.sym

@@ -1,6 +1,7 @@
 SDL3_0.0.0 {
   global:
     JNI_OnLoad;
+    SDL_DYNAPI_entry;
     SDL_AddEventWatch;
     SDL_AddGamepadMapping;
     SDL_AddGamepadMappingsFromRW;