Use fields in hidden native DOM classes instead of getters/setters.

client/dom/generated/src/frog/HTMLModElement.dart

 
 class _HTMLModElementJs extends _HTMLElementJs implements HTMLModElement native "*HTMLModElement" {
 
-  String get cite() native "return this.cite;";
+  String cite;
 
-  void set cite(String value) native "this.cite = value;";
-
-  String get dateTime() native "return this.dateTime;";
-
-  void set dateTime(String value) native "this.dateTime = value;";
+  String dateTime;
 }