Refactor searching text attributes.

* Allow using ApplicationRecord#attribute_matches to search text attributes,
and standardize models on using this instead of duplicating code.

* Remove restrictions that limited wildcard searches to Builders only in various places.

test/unit/forum_post_test.rb

@@ -164,8 +164,8 @@ class ForumPostTest < ActiveSupport::TestCase
 
     should "be searchable by body content" do
       post = FactoryBot.create(:forum_post, :topic_id => @topic.id, :body => "xxx")
-      assert_equal(1, ForumPost.body_matches("xxx").count)
-      assert_equal(0, ForumPost.body_matches("aaa").count)
+      assert_equal(1, ForumPost.search(body_matches: "xxx").count)
+      assert_equal(0, ForumPost.search(body_matches: "aaa").count)
     end
 
     should "initialize its creator" do