web: implement mainResolveAvatarUrl via js getByName

Signed-off-by: 21pages <sunboeasy@gmail.com>

flutter/lib/web/bridge.dart

@@ -2034,5 +2034,9 @@ class RustdeskImpl {
     return false;
   }
 
+  String mainResolveAvatarUrl({required String avatar, dynamic hint}) {
+    return js.context.callMethod('getByName', ['resolve_avatar_url', avatar])?.toString() ?? avatar;
+  }
+
   void dispose() {}
 }