refactor: Make Logger.forEach compatible with both rxjs 6 and 7.

Some build environments build angular with rxjs 7, and see build
failures due to this file.

(cherry picked from commit c3a3871)

packages/angular_devkit/core/src/logger/logger.ts

@@ -164,7 +164,7 @@ export class Logger extends Observable<LogEntry> implements LoggerApi {
 
   override forEach(
     next: (value: LogEntry) => void,
-    promiseCtor?: PromiseConstructorLike,
+    promiseCtor: PromiseConstructorLike = Promise,
   ): Promise<void> {
     return this._observable.forEach(next, promiseCtor);
   }