TokenizingTextBox does not unselect all Tokens on LostFocus

### Describe the bug

If a Token is selected (higlighted with blue) it will loose that focus and higlight if the `AutoSuggestTextBox `gets the focus.

But if the TokenizingTextBox looses its focus a selected Token will still retain its selected status and remains highlighted.

TokenizingTextBox.cs

```
private void TokenizingTextBoxItem_LostFocus(object sender, RoutedEventArgs e)
{
// Keep track of our currently focused textbox
[ ... ]

DeselectAllTokensAndText();
}
```

Adding the `DeselectAllTokensAndText();` should fix that.

### Steps to reproduce

```text
- create a Token
- click on it
- click on a TextBox other than the TokenizingTextBox containng the Token
```

### Expected behavior

All Tokens should be unfocused too if the `TokenizingTextBox `looses its focus.

### Screenshots

_No response_

### Code Platform

- [ ] UWP
- [X] WinAppSDK / WinUI 3
- [ ] Web Assembly (WASM)
- [ ] Android
- [ ] iOS
- [ ] MacOS
- [ ] Linux / GTK

### Windows Build Number

- [ ] Windows 10 1809 (Build 17763)
- [ ] Windows 10 1903 (Build 18362)
- [ ] Windows 10 1909 (Build 18363)
- [ ] Windows 10 2004 (Build 19041)
- [ ] Windows 10 20H2 (Build 19042)
- [ ] Windows 10 21H1 (Build 19043)
- [ ] Windows 10 21H2 (Build 19044)
- [ ] Windows 10 22H2 (Build 19045)
- [X] Windows 11 21H2 (Build 22000)
- [ ] Other (specify)

### Other Windows Build number

_No response_

### App minimum and target SDK version

- [ ] Windows 10, version 1809 (Build 17763)
- [ ] Windows 10, version 1903 (Build 18362)
- [ ] Windows 10, version 1909 (Build 18363)
- [ ] Windows 10, version 2004 (Build 19041)
- [ ] Windows 10, version 2104 (Build 20348)
- [ ] Windows 11, version 22H2 (Build 22000)
- [ ] Other (specify)

### Other SDK version

_No response_

### Visual Studio Version

_No response_

### Visual Studio Build Number

_No response_

### Device form factor

_No response_

### Additional context

_No response_

### Help us help you

Yes, but only if others can assist.

Open TokenizingTextBox.cs and inspect TokenizingTextBoxItem_LostFocus, especially the existing focus-tracking logic. Reproduce the issue by selecting a token and focusing another TextBox, then verify that losing focus clears the token selection and highlighting.

Scritto dal modello di indicizzazione a partire dal testo della issue.