SetTitleBar crash under specific condition

Nobody has claimed this yet.

### Describe the bug

I found that under specific condition, we need to wait for the element to be loaded in order to be able to call `SetTitleBar` to it instead of simply call it in window constructor, [as this documentation shows](https://learn.microsoft.com/en-us/windows/windows-app-sdk/api/winrt/microsoft.ui.xaml.window.settitlebar?view=windows-app-sdk-2.0)

Otherwise it causes the app crash.

### Why is this important?

The crash is confusing. And the document should be updated.

### Steps to reproduce the bug

1. If I specify the `Height` of this `Rectangle`, then `SetTitleBar` have to come **after** its `Loaded` event.
```xaml

```

```csharp
Bar.Loaded += (_, _) => SetTitleBar(Bar);
```

The app crashes if you do this:
```csharp
public MainWindow()
{
InitializeComponent();
ExtendsContentIntoTitleBar = true;
SetTitleBar(Bar);
}
```

2. However, if I simply replace the `Rectangle` with a `Grid` and use the exact crashing code above, it works now.
```xml

```

### Actual behavior

_No response_

### Expected behavior

_No response_

### Screenshots

_No response_

### NuGet package version

2.2.0

### Windows version

Windows 11 (24H2): Build 26100

### Additional context

_No response_

Reproduce the crash using the provided XAML and the MainWindow constructor that calls SetTitleBar on the Rectangle, then compare it with the Loaded-event version and the Grid variant. Start at SetTitleBar, ExtendsContentIntoTitleBar, and the Rectangle's Loaded event; done means identifying the condition, preventing the crash, and updating the referenced documentation if appropriate.

Written by the indexing model from the issue text.