feat(http): introduce provideHttpClientTesting provider function (#47502)

This commit introduces the `provideHttpClientTesting()` function as an
alternative to the `HttpClientTestingModule` (in fact, the NgModule is
converted internally to just use the new provider function).

PR Close #47502

packages/common/http/testing/src/module.ts

@@ -6,11 +6,10 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {HttpBackend, HttpClientModule} from '@angular/common/http';
+import {HttpClientModule} from '@angular/common/http';
 import {NgModule} from '@angular/core';
 
-import {HttpTestingController} from './api';
-import {HttpClientTestingBackend} from './backend';
+import {provideHttpClientTesting} from './provider';
 
 
 /**
@@ -25,9 +24,7 @@ import {HttpClientTestingBackend} from './backend';
     HttpClientModule,
   ],
   providers: [
-    HttpClientTestingBackend,
-    {provide: HttpBackend, useExisting: HttpClientTestingBackend},
-    {provide: HttpTestingController, useExisting: HttpClientTestingBackend},
+    provideHttpClientTesting(),
   ],
 })
 export class HttpClientTestingModule {

packages/common/http/testing/src/provider.ts

@@ -0,0 +1,22 @@
+/**
+ * @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
+ */
+
+import {HttpBackend, HttpClientModule} from '@angular/common/http';
+import {NgModule, Provider} from '@angular/core';
+
+import {HttpTestingController} from './api';
+import {HttpClientTestingBackend} from './backend';
+
+
+export function provideHttpClientTesting(): Provider[] {
+  return [
+    HttpClientTestingBackend,
+    {provide: HttpBackend, useExisting: HttpClientTestingBackend},
+    {provide: HttpTestingController, useExisting: HttpClientTestingBackend},
+  ];
+}