docs: fix/improve example for singleton-services guide (#21589)

PR Close #21589

aio/content/examples/ngmodules/src/app/app.module.ts

@@ -4,22 +4,20 @@ import { FormsModule } from '@angular/forms';
 import { HttpModule } from '@angular/http';
 
 /* App Root */
-import { AppComponent }   from './app.component';
+import { AppComponent } from './app.component';
 
 /* Feature Modules */
-import { ContactModule }    from './contact/contact.module';
-import { CoreModule }       from './core/core.module';
+import { ContactModule } from './contact/contact.module';
+// #docregion import-for-root
+import { CoreModule } from './core/core.module';
+// #enddocregion import-for-root
 
 /* Routing Module */
 import { AppRoutingModule } from './app-routing.module';
 
 
-
+// #docregion import-for-root
 @NgModule({
-  declarations: [
-    AppComponent
-  ],
-  // #docregion import-for-root
   imports: [
     BrowserModule,
     ContactModule,
@@ -28,6 +26,11 @@ import { AppRoutingModule } from './app-routing.module';
   ],
   // #enddocregion import-for-root
   providers: [],
+  declarations: [
+    AppComponent
+  ],
   bootstrap: [AppComponent]
+  // #docregion import-for-root
 })
 export class AppModule { }
+// #enddocregion import-for-root

aio/content/examples/ngmodules/src/app/core/core.module.ts

@@ -1,31 +1,34 @@
-/* tslint:disable:member-ordering no-unused-variable */
- // #docregion whole-core-module
-import {
-  ModuleWithProviders, NgModule,
-  Optional, SkipSelf }       from '@angular/core';
+// #docregion whole-core-module
+import { ModuleWithProviders, NgModule, Optional, SkipSelf } from '@angular/core';
 
-import { CommonModule }      from '@angular/common';
+import { CommonModule } from '@angular/common';
 
-import { TitleComponent }    from './title.component';
-import { UserService }       from './user.service';
+import { TitleComponent } from './title.component';
+// #docregion user-service
+import { UserService } from './user.service';
+// #enddocregion user-service
 import { UserServiceConfig } from './user.service';
 
+
+// #docregion user-service
 @NgModule({
+  // #enddocregion user-service
   imports:      [ CommonModule ],
   declarations: [ TitleComponent ],
   exports:      [ TitleComponent ],
+  // #docregion user-service
   providers:    [ UserService ]
 })
 export class CoreModule {
- // #docregion ctor
+  // #enddocregion user-service
+  // #docregion ctor
   constructor (@Optional() @SkipSelf() parentModule: CoreModule) {
     if (parentModule) {
       throw new Error(
         'CoreModule is already loaded. Import it in the AppModule only');
     }
   }
-// #enddocregion ctor
-
+  // #enddocregion ctor
 
   // #docregion for-root
   static forRoot(config: UserServiceConfig): ModuleWithProviders {
@@ -36,9 +39,8 @@ export class CoreModule {
       ]
     };
   }
-
   // #enddocregion for-root
+  // #docregion user-service
 }
-
+// #enddocregion user-service
 // #enddocregion whole-core-module
-