Added dart support code

lib/modal_progress_hud_nsn_web.dart

@@ -0,0 +1,26 @@
+// In order to *not* need this ignore, consider extracting the "web" version
+// of your plugin as a separate package, instead of inlining it in the same
+// package as the core of your plugin.
+// ignore: avoid_web_libraries_in_flutter
+import 'dart:html' as html show window;
+
+import 'package:flutter_web_plugins/flutter_web_plugins.dart';
+
+import 'modal_progress_hud_nsn_platform_interface.dart';
+
+/// A web implementation of the ModalProgressHudNsnPlatform of the ModalProgressHudNsn plugin.
+class ModalProgressHudNsnWeb extends ModalProgressHudNsnPlatform {
+  /// Constructs a ModalProgressHudNsnWeb
+  ModalProgressHudNsnWeb();
+
+  static void registerWith(Registrar registrar) {
+    ModalProgressHudNsnPlatform.instance = ModalProgressHudNsnWeb();
+  }
+
+  /// Returns a [String] containing the version of the platform.
+  @override
+  Future<String?> getPlatformVersion() async {
+    final version = html.window.navigator.userAgent;
+    return version;
+  }
+}