[WIP] Try adding signal handler ops

[kt3k]

This PR tries to add signal handler APIs. This PR depends on tokio::signal::unix module (v0.2.6) and it supports only unix environment.

This PR adds the following JS APIs:

Streaming API

for await (const _ for Deno.signal(Deno.Signal.SIGTERM)) {
  console.log("SIGTERM received!");
}

Promise API

await Deno.signal(Deno.Signal.SIGTERM);
console.log("SIGTERM!");

and also the stream can be disposed:

const sig = Deno.signal(Deno.Signal.SIGTERM);
setTimeout(() => { sig.dispose(); }, 5000);

for await (const _ for sig) {
  console.log("SIGTERM received!");
}

The above for-await loop exits after 5000ms.

This PR also adds the following shorthand functions:

Deno.signals.alarm(); // for SIGALRM
Deno.signals.child(); // for SIGCHLD
Deno.signals.hungup(); // for SIGHUP
Deno.signals.info(); // for SIGINFO
Deno.signals.interrupt(); // for SIGINT
Deno.signals.io(); // for SIGIO
Deno.signals.pipe(); // for SIGPIPE
Deno.signals.quit(); // for SIGQUIT
Deno.signals.terminate(); // for SIGTERM
Deno.signals.userDefined1(); // for SIGUSR1
Deno.signals.userDefined2(); // for SIGURS2
Deno.signals.windowChange(); // for SIGWINCH

These short hand names are inspired by methods of tokio::signal::unix::SignalKind.

---

This PR adds 3 ops:

• op_bind_signal (start watching signals)
• op_poll_singal (poll single signal)
• op_unbind_signal (stop watching signals)

And 1 resource:

• SignalStreamResource

remaining tasks:

• unit tests
• add docs/examples
• add all shorthand methods
• update lib.deno_runtime.d.ts
• fix panic at sig.dispose()
• for-await loop doesn't end after sig.dispose() -> now it works.
• modify handling of pending_ops

---

First I started with the API design loosely following the suggestion by @sholladay at the comment ( #2339 (comment) ), and then I changed it a little inspired by tokio's naming of SignalKind shorthands https://tokio-rs.github.io/tokio/doc/src/tokio/signal/unix.rs.html#82

---

closes #2339

[axetroy]

Should we support listening for multiple signals?

I think this is still useful, ref Golang

quit := make(chan os.Signal)
signal.Notify(quit, os.Kill, syscall.SIGHUP, syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT)

go func() {
	<-quit
        // do staff
	os.Exit(1)
}()

defer signal.Stop(quit)

for await (const signal for Deno.signal(Deno.Signal.SIGTERM, Deno.Signal.SIGINT, Deno.Signal.SIGHUP)) {
  console.log(`receive ${signal}`);
}

[kt3k]

@axetroy I prefer to keep Deno.signal to handle only one signal because the underlying tokio API only supports one kind of signal for each call. I think we can provide that kind of API in std.

[kt3k]

I'm a little stuck at the task modify handling of pending_ops (We need to ignore pending poll_signal async ops when checking the poll result of pending_ops, which is what Kevin did in #2735 with AsyncOptional ops). I think that task requires a lot of code change. Maybe it's better to try that task alone first (That can be done independently of this PR). Except that point, I think this PR is almost finished.