AdvancedCollectionView is not NULL annotated correctly

### Describe the bug

While this

```cs
AdvancedCollectionView acv = new AdvancedCollectionView();
acv.Add(null);
```

is working as the underlying source is an IList which supports this behaviour, all the methods in `AdvanceCollectionView` are missing the null annotations. Nevertheless this code, after updating to v8 now displays a warning: `CS8625 Cannot convert null literal to non-nullable reference type.`

### Steps to reproduce

```text
object? item = null;
AdvancedCollectionView acv = new AdvancedCollectionView();
acv.Add(item); // <- warning here
acv.Contains(item); // <- warning here
```

### Expected behavior

Expected behaviour is as it was before v8, no warnings.

### 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)
- [X] 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)
- [X] 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

_No response_

### Device form factor

Desktop

### Additional context

_No response_

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