Extensions must be reloaded to initialize collection in PropertyGrid

[RoboDoig]

Description

In some cases, a C# extension that contains a collection (e.g. List) as a property may not initialise its collection when added to the workflow.

Steps to reproduce

1. Create a new bonsai environment
2. Create a CSharpSource as an extension and create an operator with a collection property:

using Bonsai;
using System;
using System.ComponentModel;
using System.Collections.Generic;
using System.Linq;
using System.Reactive.Linq;

[Combinator]
[Description("")]
[WorkflowElementCategory(ElementCategory.Source)]
public class SourceScript
{
    public List<double> Collection {get; set;}
    public IObservable<int> Process()
    {
        return Observable.Never(0);
    }
}

3. Reload extensions in the editor, the collection for this operator should be editable
4. Add a new instance of this operator to the workflow, the collection on the new operator is not editable/saveable until extensions are reloaded.

Bonsai version

2.9.1

Additional context

No response

[RoboDoig]

Feedback from @glopesdev - This is really only a problem with extensions. Normally need to have:

public List<double> Collection = new List<double>();

which can't be done currently in extensions so instead need to have a constructor:

public SourceScript() {
    Collection = new List<double>();
}