FEATURE: Autotag watched words (#12244)

New topics with be matched against a set of watched words and be
tagged accordingly.

app/services/word_watcher.rb

@@ -8,7 +8,7 @@ class WordWatcher
 
   def self.words_for_action(action)
     words = WatchedWord.where(action: WatchedWord.actions[action.to_sym]).limit(1000)
-    if action.to_sym == :replace
+    if action.to_sym == :replace || action.to_sym == :tag
       words.pluck(:word, :replacement).to_h
     else
       words.pluck(:word)
@@ -31,7 +31,7 @@ class WordWatcher
   def self.word_matcher_regexp(action, raise_errors: false)
     words = get_cached_words(action)
     if words
-      if action.to_sym == :replace
+      if action.to_sym == :replace || action.to_sym == :tag
         words = words.keys
       end
       words = words.map do |w|
@@ -110,4 +110,12 @@ class WordWatcher
       false
     end
   end
+
+  def matches?(word)
+    if SiteSetting.watched_words_regular_expressions?
+      Regexp.new(word).match?(@raw)
+    else
+      @raw.include?(word)
+    end
+  end
 end