Fix unable to type cultural character (#15394)

Check KeySymbol before return null in TryCreateRawKeyEventArgs to prevent skipping cultural character.

Co-authored-by: CKPhong <phong.chung@itd.com.vn>

src/Windows/Avalonia.Win32/WindowImpl.AppWndProc.cs

@@ -1191,12 +1191,11 @@ namespace Avalonia.Win32
             var keyData = ToInt32(lParam);
             var key = KeyInterop.KeyFromVirtualKey(virtualKey, keyData);
             var physicalKey = KeyInterop.PhysicalKeyFromVirtualKey(virtualKey, keyData);
+            var keySymbol = KeyInterop.GetKeySymbol(virtualKey, keyData);
 
-            if (key == Key.None && physicalKey == PhysicalKey.None)
+            if (key == Key.None && physicalKey == PhysicalKey.None && string.IsNullOrWhiteSpace(keySymbol))
                 return null;
 
-            var keySymbol = KeyInterop.GetKeySymbol(virtualKey, keyData);
-
             return new RawKeyEventArgs(
                 WindowsKeyboardDevice.Instance,
                 timestamp,