refactor(facade): move isPromise to core private (#10573)

modules/@angular/core/src/util/lang.ts

@@ -0,0 +1,13 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+export function isPromise(obj: any): obj is Promise<any> {
+  // allow any Promise/A+ compliant thenable.
+  // It's up to the caller to ensure that obj.then conforms to the spec
+  return !!obj && typeof obj.then === 'function';
+}