Support async delegates for WaitFor*

[radmorecameron]

Is the feature request related to a problem? Please elaborate.

Yes, some of our state checking logic involves invoking an async method.

** A clear and concise description of what the problem is. **
WaitForStateAsync (and all other WaitFor*Asyncs) don't support async lambdas.

The suggested solution

Allow passing a Func<bool, Task> so async lambda can be used.

Additional Context
Minimum repro:

var myCut = RenderComponent<MyComponent>();
await myCut .WaitForStateAsync(async () => {
    return await myCut .CheckStateAsync();
});

// MyComponent

<div>
</div>
@code {
   public async Task<boolean> CheckStateAsync() {
     // async state checking code
   }
}

[radmorecameron]

I'm willing to take a look into supporting this