Add support for combining NotifyParentPropertyAttribute and ObservablePropertyAttribute

### Overview

`System.ComponentModel.NotifyParentPropertyAttribute` can only decorate a property but a `ObservableProperty` must be defined as a field so that a property can be generated automatically.

To allow them to work together, we should either provide a CommunityToolkit implementation of `NotifyParentPropertyAttribute` or allow `ObservablePropertyAttribute` to be used with a partial property (https://github.com/CommunityToolkit/dotnet/issues/555).

For now, the latter is infeasible as C# does not allow partial properties.

### API breakdown

```csharp
namespace CommunityToolkit.Mvvm.ComponentModel;

[AttributeUsage(AttributeTargets.Field, AllowMultiple = false, Inherited = false)]
public sealed class NotifyParentPropertyAttribute : Attribute
{
public NotifyParentPropertyAttribute(bool notifyParent)
{
NotifyParent = notifyParent;
}

public bool NotifyParent { get; }
}
```

### Usage example

```csharp
public partial class ChildModel : ObservableObject
{
[ObservableProperty]
[NotifyParentChanged(true)]
private string _name;
}

public partial class ParentModel : ObservableObject
{
[ObservableProperty]
private ChildModel _child = new ();
}
```

When the `Child.Name` property gets updated, the `ParentModel` should be notified for the change of the `Child` property, i.e., `OnPropertyChanged(nameof(Child))` should be called.
```csharp
var parentModel = new ParentModel();
parentModel.Child.Name = "something"; // should call OnPropertyChanged(nameof(Child))
```

### Breaking change?

No

### Alternatives

Currently one has to choose between `[NotifyParentChanged(true)]` and `[ObservableProperty]`.

### Additional context

_No response_

### Help us help you

Yes, but only if others can assist