VoiceCalling demo does not compile

> Please provide us with the following information:
> ---------------------------------------------------------------

### This issue is for a: (mark with an `x`)
```
- [ X] bug report -> please search issues before submitting
- [ ] feature request
- [ ] documentation issue or request
- [ ] regression (a behavior that used to work and stopped in a new release)
```

### Minimal steps to reproduce
> Checkout and compile https://github.com/Azure-Samples/communication-services-dotnet-quickstarts/tree/main/VoiceCalling

### Any log messages given by the failure
> Observe that compilation fails. That is because a few files are missing. e.g. App.xaml, App.cs

### Expected/desired behavior
> The demo compiles

### OS and Version?
> N.a. The problem happens when you compile the demo

### Versions
> head of the main branch

### Mention any other details that might be useful

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