refactor(router): compatibility with typescript strict flag (#30993)

As part of FW-1265, the `@angular/router` package is made compatible
with the TypeScript `--strict` flag. Read more about the strict flag [here](https://www.typescriptlang.org/docs/handbook/compiler-options.html)

PR Close #30993

packages/router/src/directives/router_link.ts

@@ -11,7 +11,7 @@ import {Attribute, Directive, ElementRef, HostBinding, HostListener, Input, OnCh
 import {Subscription} from 'rxjs';
 
 import {QueryParamsHandling} from '../config';
-import {NavigationEnd, RouterEvent} from '../events';
+import {Event, NavigationEnd} from '../events';
 import {Router} from '../router';
 import {ActivatedRoute} from '../router_state';
 import {UrlTree} from '../url_tree';
@@ -220,7 +220,7 @@ export class RouterLinkWithHref implements OnChanges, OnDestroy {
   constructor(
       private router: Router, private route: ActivatedRoute,
       private locationStrategy: LocationStrategy) {
-    this.subscription = router.events.subscribe((s: RouterEvent) => {
+    this.subscription = router.events.subscribe((s: Event) => {
       if (s instanceof NavigationEnd) {
         this.updateTargetUrlAndHref();
       }

packages/router/src/directives/router_link_active.ts

@@ -9,7 +9,7 @@
 import {AfterContentInit, ContentChildren, Directive, ElementRef, Input, OnChanges, OnDestroy, Optional, QueryList, Renderer2, SimpleChanges} from '@angular/core';
 import {Subscription} from 'rxjs';
 
-import {NavigationEnd, RouterEvent} from '../events';
+import {Event, NavigationEnd} from '../events';
 import {Router} from '../router';
 
 import {RouterLink, RouterLinkWithHref} from './router_link';
@@ -95,7 +95,7 @@ export class RouterLinkActive implements OnChanges,
       private router: Router, private element: ElementRef, private renderer: Renderer2,
       @Optional() private link?: RouterLink,
       @Optional() private linkWithHref?: RouterLinkWithHref) {
-    this.subscription = router.events.subscribe((s: RouterEvent) => {
+    this.subscription = router.events.subscribe((s: Event) => {
       if (s instanceof NavigationEnd) {
         this.update();
       }

packages/router/src/router_module.ts

@@ -16,7 +16,7 @@ import {Route, Routes} from './config';
 import {RouterLink, RouterLinkWithHref} from './directives/router_link';
 import {RouterLinkActive} from './directives/router_link_active';
 import {RouterOutlet} from './directives/router_outlet';
-import {RouterEvent} from './events';
+import {Event} from './events';
 import {RouteReuseStrategy} from './route_reuse_strategy';
 import {ErrorHandler, Router} from './router';
 import {ROUTES} from './router_config_loader';
@@ -444,7 +444,7 @@ export function setupRouter(
 
   if (opts.enableTracing) {
     const dom = getDOM();
-    router.events.subscribe((e: RouterEvent) => {
+    router.events.subscribe((e: Event) => {
       dom.logGroup(`Router Event: ${(<any>e.constructor).name}`);
       dom.log(e.toString());
       dom.log(e);

packages/router/src/utils/collection.ts

@@ -88,11 +88,14 @@ export function waitForMap<A, B>(
     }
   });
 
-  // Closure compiler has problem with using spread operator here. So just using Array.concat.
-  return of .apply(null, waitHead.concat(waitTail)).pipe(concatAll(), lastValue(), map(() => res));
+  // Closure compiler has problem with using spread operator here. So we use "Array.concat".
+  // Note that we also need to cast the new promise because TypeScript cannot infer the type
+  // when calling the "of" function through "Function.apply"
+  return (of .apply(null, waitHead.concat(waitTail)) as Observable<Observable<B>>)
+      .pipe(concatAll(), lastValue(), map(() => res));
 }
 
-export function wrapIntoObservable<T>(value: T | NgModuleFactory<T>| Promise<T>| Observable<T>) {
+export function wrapIntoObservable<T>(value: T | Promise<T>| Observable<T>): Observable<T> {
   if (isObservable(value)) {
     return value;
   }