FIX: Change base importer to create new Bookmark records (#9603)

Also add a spec and fixture with a mock importer that we can use to test the create_X methods of the base importer

script/import_scripts/base.rb

@@ -606,9 +606,10 @@ class ImportScripts::Base
           skipped += 1
           puts "Skipping bookmark for user id #{params[:user_id]} and post id #{params[:post_id]}"
         else
-          result = PostActionCreator.create(user, post, :bookmark)
-          created += 1 if result.success?
-          skipped += 1 if result.failed?
+          result = BookmarkManager.new(user).create(post_id: post.id)
+
+          created += 1 if result.errors.none?
+          skipped += 1 if result.errors.any?
         end
       end