[cli][next] Removed --forceExit from jest args (#8718)

Remove `--forceExit` and wait for the child `vc dev` process to close
before continuing.

Listen to the `'close'` event instead of `'exit'` to ensure stdio has
been flushed and closed before continuing.

Some tests cause `vc dev` to spawn child processes that in turn spawn
nested child processes that do not exit when the parent exits, so a
`nukeProcessTree()` helper was added to ensure all spawned processes are
cleaned up. Furthermore, some of the nested child processes don't
respond well to `SIGTERM` and we need to use `SIGKILL` if `SIGTERM`
doesn't do the job.

I uncovered a larger issue exposed by removing the `--forceExit` flag.
The go builder uses `go run` to build and run the go-based serverless
function. Turns out that `go run` will build the executable, then spawn
it with a parent process id (ppid) of `1` (launchd) on macOS. This means
that the go serverless function executable is not detected as a child
process of `vc dev` and won't be cleaned up, yet has inherited `stdout`
and `stderr` keeping Jest alive. The solution is to explicitly `go
build` the serverless executable, then run it.

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#### Tests

- [x] The code changed/added as part of this PR has been covered with
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Co-authored-by: Sean Massa <EndangeredMassa@gmail.com>

packages/cli/src/util/dev/server.ts

@@ -1026,7 +1026,7 @@ export default class DevServer {
     debug(`Killing builder dev server with PID ${pid}`);
     this.devServerPids.delete(pid);
     try {
-      process.kill(pid, 'SIGTERM');
+      await treeKill(pid);
       debug(`Killed builder dev server with PID ${pid}`);
     } catch (err) {
       debug(`Failed to kill builder dev server with PID ${pid}: ${err}`);
@@ -2279,6 +2279,10 @@ export default class DevServer {
 
     p.on('exit', (code, signal) => {
       this.output.debug(`Dev command exited with "${signal || code}"`);
+    });
+
+    p.on('close', (code, signal) => {
+      this.output.debug(`Dev command closed with "${signal || code}"`);
       this.devProcessOrigin = undefined;
     });