Add fullscreen toggle functionality and update popover alignment (#773)

* fix: update Height binding and add VerticalAlignment to fullscreen popover.

* feat: add fullscreen toggle functionality with F11 key.

demo/Semi.Avalonia.Demo/Views/MainWindow.axaml.cs

@@ -1,11 +1,38 @@
 using Avalonia.Controls;
+using Avalonia.Input;
 
 namespace Semi.Avalonia.Demo.Views;
 
 public partial class MainWindow : Window
 {
+    private WindowState _stateBeforeFullScreen = WindowState.Normal;
+
     public MainWindow()
     {
         InitializeComponent();
+        KeyDown += FullScreenKeyDown;
+    }
+
+    private void FullScreenKeyDown(object? sender, KeyEventArgs e)
+    {
+        if (e.Key == Key.F11)
+        {
+            
+            ToggleFullScreen();
+            e.Handled = true;
+        }
+    }
+
+    private void ToggleFullScreen()
+    {
+        if (WindowState is not WindowState.FullScreen)
+        {
+            _stateBeforeFullScreen = WindowState;
+            WindowState = WindowState.FullScreen;
+        }
+        else
+        {
+            WindowState = _stateBeforeFullScreen;
+        }
     }
 }