Windows.Storage.Pickers.FileSavePicker.FileTypeChoices.Add throw System.InvalidCastException: 'Specified cast is not valid.' with PublishAOT=true

@manodasanW is already working on this.

Since Sep 26, 2024.

### Describe the bug

Windows.Storage.Pickers.FileSavePicker.FileTypeChoices.Add throw System.InvalidCastException: 'Specified cast is not valid.' with PublishAOT=true
With PublishAOT=false everything works fine.

### Steps to reproduce the bug

1. Create new WinAppSDK project
2. Add `10.0.22621.45` and `true` to csproj
3. Add to myButton_Click
```
var picker = new Windows.Storage.Pickers.FileSavePicker();
WinRT.Interop.InitializeWithWindow.Initialize(picker, WinRT.Interop.WindowNative.GetWindowHandle(this));
picker.FileTypeChoices.Add("Text file", [".txt"]);
picker.SuggestedStartLocation = Windows.Storage.Pickers.PickerLocationId.DocumentsLibrary;
var file = await picker.PickSaveFileAsync();
```

### Expected behavior

After clicking on the button, the Save File dialog box should be displayed

### Screenshots

_No response_

### NuGet package version

Windows App SDK 1.6.0: 1.6.240829007

### Packaging type

Packaged (MSIX)

### Windows version

Insider Build (xxxxx)

### IDE

Visual Studio 2022-preview

### Additional context

_No response_