Improve Angular Testing Library API documentation

I am new to Angular Testing and stumbled across some misunderstandings while writing my first tests. I would like to help you improve it, so let's start collecting the issues. 🙂

1. The example for the declarations (within RenderOptions) is wrong. It configures the providers. Furthermore there is no descriptions for the providers option. https://testing-library.com/docs/angular-testing-library/api#declarations
2. We might also add a note which of the RenderOptions are passed to the Angular TestBed. Or even separate those from the added render properties.
3. Explaining that this library still works with the core testing functionality of Angular under the hood will also help to implement non-standard situations. For example in one test I needed to interact with a service. This can be done with the Angular TestBed: TestBed.get(TargetService).init();

從連結的 RenderOptions 頁面上的 Angular Testing Library API 文件開始。檢查 declarations 範例，加入缺少的 providers 描述，並釐清哪些選項會傳遞給 Angular TestBed，以及 TestBed 如何支援非標準情況。當範例和說明性註解準確涵蓋這些要點時，即可視為完成。