refactor(testing): introduce new testing api to support ng modules

BREAKING CHANGE:
- deprecations:
  * `withProviders`, use `TestBed.withModule` instead
  * `addProviders`, use `TestBed.configureTestingModule` instead
  * `TestComponentBuilder`, use `TestBed.configureTestModule` / `TestBed.override...` / `TestBed.createComponent` instead.

Closes #10354

modules/@angular/core/testing/metadata_override.ts

@@ -0,0 +1,18 @@
+/**
+ * @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
+ */
+
+/**
+ * Type used for modifications to metadata
+ *
+ * @experimental
+ */
+export type MetadataOverride<T> = {
+  add?: T,
+  remove?: T,
+  set?: T
+};