feat: deprecate @angular/http in favor of @angular/common/http (#18906)

As of 5.0, @angular/http is deprecated. @angular/common/http will
be the official HTTP API in Angular going forward.

PR Close #18906

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

@@ -13,7 +13,7 @@ import {TestRequest} from './request';
 /**
  * Defines a matcher for requests based on URL, method, or both.
  *
- * @experimental
+ * @stable
  */
 export interface RequestMatch {
   method?: string;
@@ -24,7 +24,7 @@ export interface RequestMatch {
  * Controller to be injected into tests, that allows for mocking and flushing
  * of requests.
  *
- * @experimental
+ * @stable
  */
 export abstract class HttpTestingController {
   /**

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

@@ -25,7 +25,7 @@ import {TestRequest} from './request';
  * requests were made and then flush them. In the end, a verify() method asserts
  * that no unexpected requests were made.
  *
- * @experimental
+ * @stable
  */
 @Injectable()
 export class HttpClientTestingBackend implements HttpBackend, HttpTestingController {

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

@@ -18,7 +18,7 @@ import {HttpClientTestingBackend} from './backend';
  *
  * Inject `HttpTestingController` to expect and flush requests in your tests.
  *
- * @experimental
+ * @stable
  */
 @NgModule({
   imports: [

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

@@ -15,7 +15,7 @@ import {Observer} from 'rxjs/Observer';
  * This interface allows access to the underlying `HttpRequest`, and allows
  * responding with `HttpEvent`s or `HttpErrorResponse`s.
  *
- * @experimental
+ * @stable
  */
 export class TestRequest {
   /**