Port AutoFocusBehavior Behavior

### Describe the bug

`AutoFocusBehavior` behavior class is missing in the original port.

References and related links:
- https://github.com/CommunityToolkit/Windows/releases/tag/v8.0.230907
> 🔥🐉 Note: Mixing and matching these new 8.0 packages with existing Windows Community Toolkit 7.x packages, especially UI controls, can lead to issues with the namespace changes and dependencies on common code (like the Visual Tree extensions). If there's something that we haven't yet ported but you need, [open a discussion](https://github.com/CommunityToolkit/Windows/discussions) to let us know or claim it and contribute!
- [AutoFocusBehavior](https://learn.microsoft.com/en-us/dotnet/api/communitytoolkit.winui.ui.behaviors.autofocusbehavior?view=win-comm-toolkit-dotnet-7.0) class documentation
- [AutoFocusBehavior.cs](https://github.com/CommunityToolkit/WindowsCommunityToolkit/blob/winui/CommunityToolkit.WinUI.UI.Behaviors/Focus/AutoFocusBehavior.cs) source code in v7

### Steps to reproduce

```text
N/A
```

### Expected behavior

N/A

### 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)
- [ ] 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

No, I'm unable to contribute a solution.

Inizia leggendo il codice sorgente v7 AutoFocusBehavior.cs collegato e la documentazione della relativa classe, quindi individua il progetto behavior corrispondente per WinUI 3 in questo repository. Confronta i port e i test behavior esistenti, se presenti, prima di aggiungere la classe mancante; il lavoro è completato quando AutoFocusBehavior è disponibile per la piattaforma WinAppSDK / WinUI 3.

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