add Helper API to workaround shitty Avalonia API

Avalonia.EliteBGS/Helper.cs

@@ -0,0 +1,31 @@
+using Avalonia;
+using Avalonia.Controls;
+using MsBox.Avalonia;
+
+namespace EliteBGS;
+
+public class Helper {
+    public static void MessageBox(Window owner, string caption, string text) {
+        var box = MessageBoxManager
+            .GetMessageBoxStandard(caption, text)
+            ;
+        var result = box.ShowAsPopupAsync(owner);
+        result.Wait();
+    }
+
+    public static string? OpenFileDialog(Window owner) {
+        OpenFileDialog dlg = new OpenFileDialog();
+
+        dlg.AllowMultiple = false;
+
+        var result = dlg.ShowAsync(owner);
+        result.Wait();
+        var filename = result.Result;
+
+        if (filename == null || filename.Length <= 0) {
+            return null;
+        }
+
+        return filename[0];
+    }
+}