node worker_threads in electron app fails, causing pthread usage to fail

Emscripten attempts to use node's worker_threads module in an electron app BrowserWindow (`nodeIntegration: true`), which will successfully `require('worker_threads')` but attempting to contstruct a `Worker` will fail with "worker threads are not supported in this node environment".

Emscripten should either detect the electron environment and use Web workers, or prefer Web Workers in all cases.