Add fully qualified name to cref ObservableObject in xml comments for files generated by ObservableObjectGenerator

### Describe the bug

When using the ObservableObject attribute from the CommunityToolkit.Mvvm v8.3.2 package on the code behind partial class of a WPF UserControl like this:


The reference `` symbol reference is not resolved in the *.g.cs file generated by the ObservableObjectGenerator.


First, I opened a [ticket in the DocFx project](https://github.com/dotnet/docfx/issues/10259) because I found this issue working with DocFx. Analyzing the problem with a contributor from the DocFx team, I was sent over here.

**How to fix problem**
ObservableObject should be referenced by using fully qualified name.
(e,g, ``)

It probably can be fixed by changing following line.
https://github.com/CommunityToolkit/dotnet/blob/v8.3.2/src/CommunityToolkit.Mvvm/ComponentModel/ObservableObject.cs#L275

### Regression

_No response_

### Steps to reproduce

Have a look at my test project [DocFxTest](https://github.com/RobGess/DocFxTest) to reproduce this issue or follow these steps:

1. Create WPF project.
2. Add UserControl
3. Add [ObservableObject] attribute to partial class *.xaml.cs of the UserControl.
4. Check SourceGenerator's *.g.cs file's SetProperty method's comments.

### Expected behavior

Symbol should be resolved (and highlighted).

### Screenshots

_No response_

### IDE and version

VS 2022

### IDE version

17.11.5

### Nuget packages

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

### Nuget package version(s)

8.3.2

### Additional context

_No response_

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