fix(router): do not finish bootstrap until all the routes are resolved (#14762)

DEPRECATION:

Use `RouterModule.forRoot(routes, {initialNavigation: 'enabled'})` instead of
`RouterModule.forRoot(routes, {initialNavigtaion: true})`.

Before doing this, move the initialization logic affecting the router
from the bootstrapped component to the boostrapped module.

Similarly, use `RouterModule.forRoot(routes, {initialNavigation: 'disabled'})`
instead of `RouterModule.forRoot(routes, {initialNavigation: false})`.

Deprecated options: 'legacy_enabled', `true` (same as 'legacy_enabled'),
'legacy_disabled', `false` (same as 'legacy_disabled').

The "Router Initial Navigation" design document covers this change.
Read more here:
https://docs.google.com/document/d/1Hlw1fPaVs-PCj5KPeJRKhrQGAvFOxdvTlwAcnZosu5A/edit?usp=sharing

modules/@angular/common/src/location/platform_location.ts

@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import {InjectionToken} from '@angular/core';
 /**
  * This class should not be used directly by an application developer. Instead, use
  * {@link Location}.
@@ -50,6 +51,12 @@ export abstract class PlatformLocation {
   abstract back(): void;
 }
 
+/**
+ * @whatItDoes indicates when a location is initialized
+ * @experimental
+ */
+export const LOCATION_INITIALIZED = new InjectionToken<Promise<any>>('Location Initialized');
+
 /**
  * A serializable version of the event from onPopState or onHashChange
  *