Added SDL_GetSandbox()

This adds support for detecting whether you're running in a sandbox on macOS

src/dynapi/SDL_dynapi.sym

@@ -1182,6 +1182,7 @@ SDL3_0.0.0 {
     SDL_SetErrorV;
     SDL_GetDefaultLogOutputFunction;
     SDL_RenderDebugText;
+    SDL_GetSandbox;
     # extra symbols go here (don't modify this line)
   local: *;
 };