Added unhandledRejection event (microsoft#912)

The event "unhandledRejection" was added on process.on because when Promise is rejected and there is no catch
the error will not be thrown and process.on('uncaughtException') won't call for Node10 but it will emit "uncaughtException" for node 16.
So we need to listen to "unhandledRejection" and throw the error to make sure the error is thrown and the result will be similar.

Author: DmitriiBobreshev

node/package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "azure-pipelines-task-lib",
-  "version": "4.1.0",
+  "version": "4.2.0",
   "description": "Azure Pipelines Task SDK",
   "main": "./task.js",
   "typings": "./task.d.ts",

node/package.json

@@ -108,6 +108,20 @@ process.on('uncaughtException', (err: Error) => {
     error(String(err.stack));
 });
 
+//
+// Catching unhandled rejections from promises and rethrowing them as exceptions
+// For example, a promise that is rejected but not handled by a .catch() handler in node 10 
+// doesn't cause an uncaughtException but causes in Node 16.
+// For types definitions(Error | Any) see https://nodejs.org/docs/latest-v16.x/api/process.html#event-unhandledrejection
+//
+process.on('unhandledRejection', (reason: Error | any) => {
+    if (reason instanceof Error) {
+        throw reason;
+    } else {
+        throw new Error(reason);
+    }
+});
+
 //-----------------------------------------------------
 // Loc Helpers
 //-----------------------------------------------------