Worker thread initialization via JsTransferable

[alshdavid]

• Added JsTransferable type to allow sending values from the main thread to workers
  • This is similar to Napi's External type but can be sent to worker thread via postMessage
  • This is needed to inject things into Node worker threads (like filesystem)
• Transfering a Rust channel to the Nodejs worker so it can notify the main thread that a worker has started

💻 Examples

// Main thread
#[napi]
fn create_foo() -> napi::Result<JsTransferable<String>> {
  let my_string = "hello world".to_string();
  Ok(JsTransferable::new(my_string))
}

// Main thread
import napi from 'napi.node'

let my_string_ptr = napi.createFoo();
workerThread.postMessage(my_string_ptr);

// Worker thread
import napi from 'napi.node'
import { parentPort } from 'node::worker_threads'

parentPort.addEvent('message', ({ data: my_string_ptr }) => {
  napi.useFoo(my_string_ptr)
})

// Worker thread
#[napi]
fn use_foo(my_string_ptr: JsTransferable<String>) -> napi::Result<()> {
  let my_string = my_string_ptr.take()?;
  println!("{my_string}");
  Ok(())
}