Use observable collections for solution model

src/SharpIDE.Godot/Features/Common/TreeItemContainer.cs

@@ -0,0 +1,24 @@
+using System.Collections.Specialized;
+using Godot;
+using ObservableCollections;
+using SharpIDE.Application.Features.SolutionDiscovery.VsPersistence;
+
+namespace SharpIDE.Godot.Features.Common;
+
+public class TreeItemContainer
+{
+    public TreeItem? Value { get; set; }
+}
+
+public static class ObservableTreeExtensions
+{
+    public static ObservableHashSet<T> WithInitialPopulation<T>(this ObservableHashSet<T> hashSet, Action<ViewChangedEvent<T, TreeItemContainer>> func) where T : class
+    {
+        foreach (var existing in hashSet)
+        {
+            var viewChangedEvent = new ViewChangedEvent<T, TreeItemContainer>(NotifyCollectionChangedAction.Add, (existing, new TreeItemContainer()), (null!, null!), 0, 0, new SortOperation<T>());
+            func(viewChangedEvent);
+        }
+        return hashSet;
+    }
+}