FIX: Make serialized watched word regex Javascript compatible (#22010)

This change ensures Javascript compatible regex is serialized instead of
the default ruby based one.

app/serializers/watched_word_list_serializer.rb

@@ -18,7 +18,7 @@ class WatchedWordListSerializer < ApplicationSerializer
   def compiled_regular_expressions
     expressions = {}
     actions.each do |action|
-      expressions[action] = WordWatcher.serializable_word_matcher_regexp(action)
+      expressions[action] = WordWatcher.serializable_word_matcher_regexp(action, engine: :js)
     end
     expressions
   end

app/serializers/watched_word_serializer.rb

@@ -4,7 +4,7 @@ class WatchedWordSerializer < ApplicationSerializer
   attributes :id, :word, :regexp, :replacement, :action, :case_sensitive
 
   def regexp
-    WordWatcher.word_to_regexp(word)
+    WordWatcher.word_to_regexp(word, engine: :js)
   end
 
   def action