improve hardening options

packages/flutter_mozilla_components/lib/src/domain/services/gecko_pref.dart

@@ -1,3 +1,5 @@
+import 'dart:convert';
+
 import 'package:flutter_mozilla_components/src/pigeons/gecko.g.dart';
 
 final _apiInstance = GeckoPrefApi();
@@ -16,7 +18,7 @@ class GeckoPrefService {
       final value = switch (pref.value) {
         final bool x => '$x',
         final int x => '$x',
-        final String x => "'$x'", //Use single ticks to allow json
+        final String x => jsonEncode(x),
         _ => throw Exception('Unknow pref type'),
       };