Meta - Replace WPF projects with Avalonia projects

src/Artemis.UI/Screens/ProfileEditor/Panels/Properties/Timeline/TimelineGroupViewModel.cs

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+using System;
+using System.Collections.ObjectModel;
+using System.Linq;
+using Artemis.UI.Shared;
+using Artemis.UI.Shared.Services.ProfileEditor;
+using Avalonia.Controls.Mixins;
+using ReactiveUI;
+
+namespace Artemis.UI.Screens.ProfileEditor.Properties.Timeline;
+
+public class TimelineGroupViewModel : ActivatableViewModelBase
+{
+    private ObservableCollection<double>? _keyframePositions;
+    private int _pixelsPerSecond;
+
+    public TimelineGroupViewModel(PropertyGroupViewModel propertyGroupViewModel, IProfileEditorService profileEditorService)
+    {
+        PropertyGroupViewModel = propertyGroupViewModel;
+
+        this.WhenActivated(d =>
+        {
+            profileEditorService.PixelsPerSecond.Subscribe(p =>
+            {
+                _pixelsPerSecond = p;
+                UpdateKeyframePositions();
+            });
+            this.WhenAnyValue(vm => vm.PropertyGroupViewModel.IsExpanded).Subscribe(_ => UpdateKeyframePositions()).DisposeWith(d);
+            PropertyGroupViewModel.WhenAnyValue(vm => vm.IsExpanded).Subscribe(_ => this.RaisePropertyChanged(nameof(Children))).DisposeWith(d);
+        });
+    }
+
+    public PropertyGroupViewModel PropertyGroupViewModel { get; }
+
+    public ObservableCollection<ViewModelBase>? Children => PropertyGroupViewModel.IsExpanded ? PropertyGroupViewModel.Children : null;
+
+    public ObservableCollection<double>? KeyframePositions
+    {
+        get => _keyframePositions;
+        set => RaiseAndSetIfChanged(ref _keyframePositions, value);
+    }
+
+    private void UpdateKeyframePositions()
+    {
+        KeyframePositions = new ObservableCollection<double>(PropertyGroupViewModel
+            .GetAllKeyframeViewModels(false)
+            .Select(p => p.Position.TotalSeconds * _pixelsPerSecond));
+    }
+}