fix(compiler): allow tree-shakeable injectables to depend on string tokens (#22376)

Previously the injectable compiler assumed all tree-shakeable injectables
would have dependencies that were injectables or InjectionTokens. However
old code still uses string tokens (e.g. NgUpgrade and '$injector'). Using
such tokens would cause the injectable compiler to crash.

Now, the injectable compiler can properly generate a dependency on such a
string token.

PR Close #22376

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

@@ -0,0 +1,38 @@
+/**
+ * @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, Inject, Injectable, NgModule} from '@angular/core';
+import {BrowserModule} from '@angular/platform-browser';
+import {ServerModule} from '@angular/platform-server';
+
+
+@Component({
+  selector: 'string-app',
+  template: '{{data}}',
+})
+export class AppComponent {
+  data: string;
+  constructor(service: Service) { this.data = service.data; }
+}
+
+@NgModule({
+  imports: [
+    BrowserModule.withServerTransition({appId: 'id-app'}),
+    ServerModule,
+  ],
+  declarations: [AppComponent],
+  bootstrap: [AppComponent],
+  providers: [{provide: 'someStringToken', useValue: 'works'}],
+})
+export class StringAppModule {
+}
+
+@Injectable({scope: StringAppModule})
+export class Service {
+  constructor(@Inject('someStringToken') readonly data: string) {}
+}