`process.on` is not implemented

I'd like to [gracefully shutdown my lambda](https://github.com/aws-samples/graceful-shutdown-with-aws-lambda/tree/main/nodejs-demo)

However, looks like LLRT has no `process.on('SIGTERM', ...` implemented yet
```[tasklist]
### Tasks
- [ ] implement process.on
- [ ] emit SIGTERM event
```

Start with the linked AWS Lambda Node.js demo to understand the intended graceful-shutdown behavior, then locate LLRT's process API and signal handling entry points. Implement the two listed tasks: support process.on and emit a SIGTERM event, and verify the demo's handler can run during shutdown.

Written by the indexing model from the issue text.