Adding `WaitForComponent` / `WaitForComponents`

[linkdotnet]

Rational

In today's world, we already have WaitForElement which allows waiting for an async method an retrieve an IElement from the given css-selector.

We could offer a similiar thing for components:

IRenderedComponent<MyComponent> entry = cut.WaitForComponent<MyComponent>();

In its core it is nothing more than:

public static IRenderedComponent<TComponent> WaitForComponent<TComponent>(this IRenderedComponent<IComponent> component) 
    where TComponent : IComponent
{
    component.WaitForState(component.HasComponent<TComponent>);
    return component.FindComponent<TComponent>();
}

[egil]

Pretty obvious. Let's add it, and WaitForComponents too.

[linkdotnet]

Shall we „only“ add this to v2?
Not a big thing to add in general - I would just like that we focus more on that part :)

PS: most potential for errors is updating the docs on v1 and meting them into v2. That is why I am pushing more towards v2 only