build: import in-memory-web-api project (#37182)

Moves the `angular-in-memory-web-api` project into the main repository in order to make it easier to maintain and release.

PR Close #37182

packages/misc/angular-in-memory-web-api/test/fixtures/hero-in-mem-data-service.ts

@@ -0,0 +1,79 @@
+/**
+ * @license
+ * Copyright Google LLC 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
+ */
+
+
+/**
+ * This is an example of a Hero-oriented InMemoryDbService.
+ *
+ * For demonstration purposes, it can return the database
+ * synchronously as an object (default),
+ * as an observable, or as a promise.
+ *
+ * Add the following line to `AppModule.imports`
+ *   InMemoryWebApiModule.forRoot(HeroInMemDataService) // or HeroInMemDataOverrideService
+ */
+import {Injectable} from '@angular/core';
+import {InMemoryDbService, RequestInfo} from 'angular-in-memory-web-api';
+import {Observable, of} from 'rxjs';
+import {delay} from 'rxjs/operators';
+
+interface Person {
+  id: string|number;
+  name: string;
+}
+
+interface PersonResponse {
+  heroes: Person[];
+  stringers: Person[];
+  nobodies: Person[];
+}
+
+@Injectable()
+export class HeroInMemDataService implements InMemoryDbService {
+  createDb(reqInfo?: RequestInfo):
+      Observable<PersonResponse>|Promise<PersonResponse>|PersonResponse {
+    const heroes = [
+      {id: 1, name: 'Windstorm'}, {id: 2, name: 'Bombasto'}, {id: 3, name: 'Magneta'},
+      {id: 4, name: 'Tornado'}
+    ];
+
+    const nobodies: any[] = [];
+
+    // entities with string ids that look like numbers
+    const stringers = [{id: '10', name: 'Bob String'}, {id: '20', name: 'Jill String'}];
+
+    // default returnType
+    let returnType = 'object';
+    // let returnType  = 'observable';
+    // let returnType  = 'promise';
+
+    // demonstrate POST commands/resetDb
+    // this example clears the collections if the request body tells it to do so
+    if (reqInfo) {
+      const body = reqInfo.utils.getJsonBody(reqInfo.req) || {};
+      if (body.clear === true) {
+        heroes.length = 0;
+        nobodies.length = 0;
+        stringers.length = 0;
+      }
+
+      // 'returnType` can be 'object' | 'observable' | 'promise'
+      returnType = body.returnType || 'object';
+    }
+    const db = {heroes, nobodies, stringers};
+
+    switch (returnType) {
+      case 'observable':
+        return of(db).pipe(delay(10));
+      case 'promise':
+        return new Promise(resolve => setTimeout(() => resolve(db), 10));
+      default:
+        return db;
+    }
+  }
+}