Improved unhandled rejection message

Fixes nodejs#16768

lib/internal/process/promises.js

@@ -1,7 +1,5 @@
 'use strict';
 
-const { safeToString } = process.binding('util');
-
 const promiseRejectEvent = process._promiseRejectEvent;
 const hasBeenNotifiedProperty = new WeakMap();
 const promiseToGuidProperty = new WeakMap();
@@ -60,11 +58,23 @@ function setupPromises(scheduleMicrotasks) {
   }
 
   function emitWarning(uid, reason) {
+    try {
+      if (reason instanceof Error) {
+        process.emitWarning(reason.stack, 'UnhandledPromiseRejectionWarning');
+      } else {
+        process.emitWarning(reason, 'UnhandledPromiseRejectionWarning');
+      }
+    } catch (e) {
+      // ignored
+    }
+
     const warning = new Error(
-      `Unhandled promise rejection (rejection id: ${uid}): ` +
-      safeToString(reason));
+      'Unhandled promise rejection. This error originated either by ' +
+      'throwing inside of an async function without a catch block, ' +
+      'or by rejecting a promise which was not handled with .catch(). ' +
+      `(rejection id: ${uid})`
+    );
     warning.name = 'UnhandledPromiseRejectionWarning';
-    warning.id = uid;
     try {
       if (reason instanceof Error) {
         warning.stack = reason.stack;