`Guard.IsReferenceEqualTo` should accept `T?`

### Describe the bug

Currently it seems that `Guard.IsReferenceEqualTo` requires the parameters to be non-null. I believe the signature should be changed to permit nullable types because I believe that comparison to null values is a reasonable expectation and it is supported by the underlying call to `object.ReferenceEquals`

### Regression

_No response_

### Steps to reproduce

```text
object x = null;
object y = new Object();

Guard.IsReferenceEqualTo(x,y); //produces CS8634
```

### Expected behavior

No CS8634

### Screenshots

_No response_

### IDE and version

VS 2022 Preview

### IDE version

_No response_

### Nuget packages

- [ ] CommunityToolkit.Common
- [ ] CommunityToolkit.Diagnostics
- [ ] CommunityToolkit.HighPerformance
- [ ] CommunityToolkit.Mvvm (aka MVVM Toolkit)

### Nuget package version(s)

8.2.2

### Additional context

_No response_

### Help us help you

Yes, I'd like to be assigned to work on this item