[MVVM] Don't add default parameter in attribute constructor

### Describe the bug

I have an Attribute, which constructor looks like this:

```csharp
[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = false, Inherited = false)]
public class CrossValidateAttribute : ValidationAttribute {
public CrossValidateAttribute([CallerMemberName] string? member = null) { }
}
```

The idea is to get the properties name when this gets constructed.
If I put this on a normal Property, e.g.

```csharp
[CrossValidate]
public string Foo { ... }
```

it will work and I get `Foo` as content of `member`.

But, if I put this on an `[ObservableProperty]` the generator will output this:

```csharp
[ObservableProperty]
[CrossValidate]
private string? bar;
```

```csharp
///
[global::System.CodeDom.Compiler.GeneratedCode("CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator", "8.2.0.0")]
[global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
[global::XXX.CrossValidateAttribute(null)]
public string? Bar { ... }
```

Here you can see the `XXX.CrossValidateAttribute(null)` call, which is not want I want.

Can this be done the way I want it, e.g. `XXX.CrossValidateAttribute()`?
### IDE and version

VS 2022

### IDE version

Version 17.7.6

### Nuget packages

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

### Nuget package version(s)

8.2.2

### Additional context

_No response_

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