Unhandled Microsoft.UI.Xaml.Application.Current.UnhandledException should also fire AppDomain.CurrentDomain.UnhandledException

### Describe the bug

It's really nice to have a chance to connect to `Microsoft.UI.Xaml.Application.Current.UnhandledException` and sometimes recover from it (`Handled = true`). But when that property isn't touched, I feel like the `AppDomain.CurrentDomain.UnhandledException` should fire as well.

It allows for a single collection point for crash reporting platforms...

### Steps to reproduce the bug

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### Expected behavior

UI thread exceptions also firing `AppDomain.CurrentDomain.UnhandledException` id `Handled` isn't set to `true`

### Screenshots

_No response_

### NuGet package version

None

### Windows version

_No response_

### Additional context

_No response_

Start from Microsoft.UI.Xaml.Application.Current.UnhandledException and AppDomain.CurrentDomain.UnhandledException, reproducing a UI-thread exception with Handled left unchanged and with Handled set to true. Define the behavior and verify that the AppDomain event fires only when the XAML exception is not handled, including the crash-reporting scenario described.

Written by the indexing model from the issue text.