Revert "refactor(router): remove deprecated initialNavigation options (#18781)"

This reverts commit d76761bf01.

packages/router/test/bootstrap.spec.ts

@@ -90,6 +90,48 @@ describe('bootstrap', () => {
     });
   });
 
+  it('should NOT wait for resolvers to complete when initialNavigation = legacy_enabled',
+     (done) => {
+       @Component({selector: 'test', template: 'test'})
+       class TestCmpLegacyEnabled {
+       }
+
+       @NgModule({
+         imports: [
+           BrowserModule,
+           RouterModule.forRoot(
+               [{path: '**', component: TestCmpLegacyEnabled, resolve: {test: TestResolver}}],
+               {useHash: true, initialNavigation: 'legacy_enabled'})
+         ],
+         declarations: [RootCmp, TestCmpLegacyEnabled],
+         bootstrap: [RootCmp],
+         providers: [...testProviders, TestResolver],
+         schemas: [CUSTOM_ELEMENTS_SCHEMA]
+       })
+       class TestModule {
+         constructor(router: Router) {
+           log.push('TestModule');
+           router.events.subscribe(e => log.push(e.constructor.name));
+         }
+       }
+
+       platformBrowserDynamic([]).bootstrapModule(TestModule).then(res => {
+         const router = res.injector.get(Router);
+         expect(router.routerState.snapshot.root.firstChild).toBeNull();
+         // ResolveEnd has not been emitted yet because bootstrap returned too early
+         expect(log).toEqual([
+           'TestModule', 'RootCmp', 'NavigationStart', 'RoutesRecognized', 'GuardsCheckStart',
+           'GuardsCheckEnd', 'ResolveStart'
+         ]);
+
+         router.events.subscribe((e) => {
+           if (e instanceof NavigationEnd) {
+             done();
+           }
+         });
+       });
+     });
+
   it('should not run navigation when initialNavigation = disabled', (done) => {
     @Component({selector: 'test', template: 'test'})
     class TestCmpDiabled {
@@ -120,6 +162,37 @@ describe('bootstrap', () => {
     });
   });
 
+  it('should not run navigation when initialNavigation = legacy_disabled', (done) => {
+    @Component({selector: 'test', template: 'test'})
+    class TestCmpLegacyDisabled {
+    }
+
+    @NgModule({
+      imports: [
+        BrowserModule,
+        RouterModule.forRoot(
+            [{path: '**', component: TestCmpLegacyDisabled, resolve: {test: TestResolver}}],
+            {useHash: true, initialNavigation: 'legacy_disabled'})
+      ],
+      declarations: [RootCmp, TestCmpLegacyDisabled],
+      bootstrap: [RootCmp],
+      providers: [...testProviders, TestResolver],
+      schemas: [CUSTOM_ELEMENTS_SCHEMA]
+    })
+    class TestModule {
+      constructor(router: Router) {
+        log.push('TestModule');
+        router.events.subscribe(e => log.push(e.constructor.name));
+      }
+    }
+
+    platformBrowserDynamic([]).bootstrapModule(TestModule).then(res => {
+      const router = res.injector.get(Router);
+      expect(log).toEqual(['TestModule', 'RootCmp']);
+      done();
+    });
+  });
+
   it('should not init router navigation listeners if a non root component is bootstrapped',
      (done) => {
        @NgModule({