fix: use Node's microtasks policy in node_main.cc (#23153)

Fixes #21515.

spec/fixtures/module/node-promise-timer.js

@@ -0,0 +1,23 @@
+const waitMs = (msec) => new Promise((resolve) => setTimeout(resolve, msec));
+
+const intervalMsec = 100;
+const numIterations = 2;
+let curIteration = 0;
+let promise;
+
+for (let i = 0; i < numIterations; i++) {
+  promise = (promise || waitMs(intervalMsec)).then(() => {
+    ++curIteration;
+    return waitMs(intervalMsec);
+  });
+}
+
+// https://github.com/electron/electron/issues/21515 was about electron
+// exiting before promises finished. This test sets the pending exitCode
+// to failure, then resets it to success only if all promises finish.
+process.exitCode = 1;
+promise.then(() => {
+  if (curIteration === numIterations) {
+    process.exitCode = 0;
+  }
+});