feat: easier way to destroy child processes

[marvinhagemeister]

After a debugging session regarding leaking resources in tests it turned out that a test case in the Fresh repository wasn't properly waiting for child processes to be killed.

The current way to do it should look like this:

const childProcess = new Deno.Command(...).spawn();

// Send kill signal
childProcess.kill("SIGTERM");
// Wait until it's shut down finished. This is often forgotten
await childProcess.status;

This lead us to wonder if we could provide an easier API for that. Especially, in a test suite it's not relevant how the child process is killed. You just want this thing to be destroyed. Some random ideas:

// New method
await childProcess.killAndWait();

// Make kill() return Promise, doesn't work with every signal though so meh
await childProcess.kill("SIGTERM")

// Add necessary symbols to support "using"
using childProcess = new Deno.Command(...).spawn();

[lucacasonato]

It's to be noted that with #20501 the accuracy of the op sanitizer has improved to the point where forgetting await childProcess.status will fail the test with a sanitizer error, if the sanitizers are enabled (as they are by default).

We should still ponder this, but it's less urgent now.

[magurotuna]

Now that delcaration with using is supported and ChildProcess implements AsyncDisposable, we can easily ensure child processes are destructed once they get out of scope:

await using proc = new Deno.Command(...).spawn();