StartAnimationAction throw exception when Animation is null

### Describe the bug

when `StartAnimationAction`'s `Animation` binding to a element with ElementName which has not been "loaded", if the animation is triggered, it will throw a exception

```
System.ArgumentNullException: Value cannot be null. (Parameter 'Animation')
```

### Steps to reproduce

```text
described as above
```

### Expected behavior

StartAnimationAction should ignore null value rather than throw a exception

### 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)
- [X] 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

2022

### Visual Studio Build Number

17.7.4

### Device form factor

Desktop

### Additional context

_No response_

### Help us help you

Yes, but only if others can assist.

Beginne damit, StartAnimationAction und den Codepfad zu lokalisieren, der in der WinAppSDK/WinUI 3-Implementierung die Animation-Bindung für ein nicht geladenes ElementName auflöst. Stelle den im Issue beschriebenen Auslöser für die Null-Animation nach und überprüfe anschließend, dass die Aktion den Nullwert ignoriert, ohne eine Exception auszulösen, und dass das bestehende Verhalten intakt bleibt.

Vom Indexierungsmodell aus dem Issue-Text verfasst.