feat: allow direct scoping of @Injectables to the root injector (#22185)

@Injectable() supports a scope parameter which specifies the target module.
However, it's still difficult to specify that a particular service belongs
in the root injector. A developer attempting to ensure that must either
also provide a module intended for placement in the root injector or target
a module known to already be in the root injector (e.g. BrowserModule).
Both of these strategies are cumbersome and brittle.

Instead, this commit adds a token APP_ROOT_SCOPE which provides a
straightforward way of targeting the root injector directly, without
requiring special knowledge of modules within it.

PR Close #22185

packages/compiler-cli/integrationtest/bazel/injectable_def/app/src/root.ts

@@ -0,0 +1,43 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {APP_ROOT_SCOPE, Component, Injectable, NgModule, Optional, Self} from '@angular/core';
+import {BrowserModule} from '@angular/platform-browser';
+import {ServerModule} from '@angular/platform-server';
+import {RouterModule} from '@angular/router';
+
+import {LazyModuleNgFactory} from './root_lazy.ngfactory';
+
+@Component({
+  selector: 'root-app',
+  template: '<router-outlet></router-outlet>',
+})
+export class AppComponent {
+}
+
+export function children(): any {
+  console.error('children', LazyModuleNgFactory);
+  return LazyModuleNgFactory;
+}
+
+
+@NgModule({
+  imports: [
+    BrowserModule.withServerTransition({appId: 'id-app'}),
+    ServerModule,
+    RouterModule.forRoot(
+        [
+          {path: '', pathMatch: 'prefix', loadChildren: children},
+        ],
+        {initialNavigation: 'enabled'}),
+  ],
+  declarations: [AppComponent],
+  bootstrap: [AppComponent],
+})
+export class RootAppModule {
+}

packages/compiler-cli/integrationtest/bazel/injectable_def/app/src/root_lazy.ts

@@ -0,0 +1,35 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {Component, NgModule, Optional, Self} from '@angular/core';
+import {RouterModule} from '@angular/router';
+import {Service} from './root_service';
+
+@Component({
+  selector: 'lazy-route',
+  template: '{{service}}:{{serviceInLazyInjector}}',
+})
+export class RouteComponent {
+  service: boolean;
+  serviceInLazyInjector: boolean;
+  constructor(@Optional() service: Service, @Optional() @Self() lazyService: Service) {
+    this.service = !!service;
+    this.serviceInLazyInjector = !!lazyService;
+  }
+}
+
+@NgModule({
+  declarations: [RouteComponent],
+  imports: [
+    RouterModule.forChild([
+      {path: '', pathMatch: 'prefix', component: RouteComponent},
+    ]),
+  ],
+})
+export class LazyModule {
+}

packages/compiler-cli/integrationtest/bazel/injectable_def/app/src/root_service.ts

@@ -0,0 +1,15 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {APP_ROOT_SCOPE, Injectable} from '@angular/core';
+
+@Injectable({
+  scope: APP_ROOT_SCOPE,
+})
+export class Service {
+}