feat: Add ProgressButton control and demo.

src/Avalonia/HandyControl_Avalonia/Controls/Button/ProgressButton.cs

@@ -0,0 +1,26 @@
+using Avalonia;
+using Avalonia.Controls.Primitives;
+using Avalonia.Styling;
+
+namespace HandyControl.Controls;
+
+public class ProgressButton : ToggleButton
+{
+    public static readonly StyledProperty<ControlTheme?> ProgressThemeProperty =
+        AvaloniaProperty.Register<ProgressButton, ControlTheme?>(nameof(ProgressTheme));
+
+    public static readonly StyledProperty<double> ProgressProperty =
+        AvaloniaProperty.Register<ProgressButton, double>(nameof(Progress));
+
+    public ControlTheme? ProgressTheme
+    {
+        get => GetValue(ProgressThemeProperty);
+        set => SetValue(ProgressThemeProperty, value);
+    }
+
+    public double Progress
+    {
+        get => GetValue(ProgressProperty);
+        set => SetValue(ProgressProperty, value);
+    }
+}