Pausing all threads

**Version of emscripten/emsdk:**
3.1.5

It seems that there is currently no option to pause my wasm app (ffmpeg). When executing, it spins up ~20 pthreads/workers. I would like to have an option to pause the whole thing, but with my current approach it keeps running (and sending logs via callback).

My build configuration:

```
-s EXPORTED_FUNCTIONS="[..., _emscripten_pause_main_loop, _emscripten_resume_main_loop, _emscripten_sleep]"
-s DEFAULT_LIBRARY_FUNCS_TO_INCLUDE="[emscripten_pause_main_loop, emscripten_resume_main_loop, emscripten_sleep]"
-s ASYNCIFY
-s USE_PTHREADS=1
-s PROXY_TO_PTHREAD=1
-s ENVIRONMENT=worker
-pthread
...
```

What I tried:

my-worker.js:

```js
module.pauseMainLoop(); // seems the same as module._emscripten_pause_main_loop
for(const pthread of Object.values(module.PThread.pthreads))
pthread.worker.postMessage({cmd:"pause"});
```

customized generated ffmpeg.worker.js:

```js
else if(e.data.cmd==="pause")
Module.pauseMainLoop();
```

I have also tried `module._emscripten_sleep(...)` but same result.

Is there any other approach to take preferably on javascript side, without doing heavy modifications in native code?