Implement WinUI ProgressBarHandler native events (#874)

* Implement WinUI ProgressBarHandler native events

* Enable nullable in WinUI ProgressBarHandler

src/Compatibility/Core/src/WinUI/ProgressBarRenderer.cs

@@ -87,6 +87,7 @@ void UpdateProgressColor()
 			}
 		}
 
+		[PortHandler]
 		void ProgressBarOnValueChanged(object sender, RangeBaseValueChangedEventArgs rangeBaseValueChangedEventArgs)
 		{
 			((IVisualElementController)Element)?.InvalidateMeasure(InvalidationTrigger.MeasureChanged);

src/Core/src/Handlers/ProgressBar/ProgressBarHandler.Windows.cs

@@ -1,14 +1,31 @@
-using Microsoft.UI.Xaml.Controls;
+#nullable enable
+using Microsoft.UI.Xaml.Controls;
+using Microsoft.UI.Xaml.Controls.Primitives;
 
 namespace Microsoft.Maui.Handlers
 {
 	public partial class ProgressBarHandler : ViewHandler<IProgress, ProgressBar>
 	{
 		protected override ProgressBar CreateNativeView() => new ProgressBar { Minimum = 0, Maximum = 1 };
 
+		protected override void ConnectHandler(ProgressBar nativeView)
+		{
+			nativeView.ValueChanged += OnProgressBarValueChanged;
+		}
+
+		protected override void DisconnectHandler(ProgressBar nativeView)
+		{
+			nativeView.ValueChanged -= OnProgressBarValueChanged;
+		}
+
 		public static void MapProgress(ProgressBarHandler handler, IProgress progress)	
 		{
 			handler.NativeView?.UpdateProgress(progress);
 		}
+
+		void OnProgressBarValueChanged(object? sender, RangeBaseValueChangedEventArgs rangeBaseValueChangedEventArgs)
+		{
+			VirtualView?.InvalidateMeasure();
+		}
 	}
 }