Update itemssource in PersistChanges when working with a primitive collection editor

[ykarpeev]

If I have a viewmodel that I bind to the propertygrid that has a property such as:

   public List<string> ListOfStrings
   {
       get => this.AppSettings.Strings;

       set => this.AppSettings.Strings = value;
   }

When editing the collection I do not see the "set" called when the changes are made. This change allows for it to happen.