Move ActsAsTaggableOn::Tag overrides to initializer

This is to prepare for zeitwerk autoloader, and the old file couldn't be
autoloaded anyway, so the easiest is to just move it out of the models
folder.

app/assets/javascripts/app/helpers/text_formatter.js

@@ -43,7 +43,7 @@
 
     var hashtagPlugin = window.markdownitHashtag;
     md.use(hashtagPlugin, {
-      // compare tag_text_regexp in app/models/acts_as_taggable_on-tag.rb
+      // compare tag_text_regexp in config/initializers/acts_as_taggable_on.rb
       hashtagRegExp: "[" + PosixBracketExpressions.word +
                            "\\u055b" + // Armenian emphasis mark
                            "\\u055c" + // Armenian exclamation mark

app/assets/javascripts/app/views/tag_following_list_view.js

@@ -48,7 +48,7 @@ app.views.TagFollowingList = app.views.Base.extend({
     if(evt){ evt.preventDefault(); }
 
     var name = this.$(".tag_input").val();
-    // compare tag_text_regexp in app/models/acts_as_taggable_on-tag.rb
+    // compare tag_text_regexp in config/initializers/acts_as_taggable_on.rb
     var normalizedName = (name === "<3" ? name : name.replace(
         new RegExp("[^" + PosixBracketExpressions.alnum + "_\\-]+", "gi"), "").toLowerCase());
 

app/models/acts_as_taggable_on-tag.rb

@@ -1,25 +0,0 @@
-# frozen_string_literal: true
-
-module ActsAsTaggableOn
-  class Tag
-
-    self.include_root_in_json = false
-
-    def self.tag_text_regexp
-      @tag_text_regexp ||= "[[:word:]]\u055b\u055c\u055e\u058a_-"
-    end
-
-    def self.autocomplete(name)
-      where("name LIKE ?", "#{name.downcase}%").order("name ASC")
-    end
-
-    def self.normalize(name)
-      if name =~ /^#?<3/
-        # Special case for love, because the world needs more love.
-        '<3'
-      elsif name
-        name.gsub(/[^#{self.tag_text_regexp}]/, '').downcase
-      end
-    end
-  end
-end

config/initializers/acts_as_taggable_on.rb

@@ -1,4 +1,26 @@
 # frozen_string_literal: true
 
-require 'models/acts_as_taggable_on-tag'
+module ActsAsTaggableOn
+  class Tag
+    self.include_root_in_json = false
+
+    def self.tag_text_regexp
+      @tag_text_regexp ||= "[[:word:]]\u055b\u055c\u055e\u058a_-"
+    end
+
+    def self.autocomplete(name)
+      where("name LIKE ?", "#{name.downcase}%").order("name ASC")
+    end
+
+    def self.normalize(name)
+      if name =~ /^#?<3/
+        # Special case for love, because the world needs more love.
+        "<3"
+      elsif name
+        name.gsub(/[^#{tag_text_regexp}]/, "").downcase
+      end
+    end
+  end
+end
+
 ActsAsTaggableOn.force_lowercase = true