FIX: Update user stat counts when post/topic visibility changes. (#15883)

Breakdown of fixes in this commit:

* `UserStat#topic_count` was not updated when visibility of
the topic changed.

* `UserStat#post_count` was not updated when post was hidden or
unhidden.

* `TopicConverter` was only incrementing or decrementing the counts by 1
even if a user has multiple posts in the topic.

* The commit turns off the verbose logging by default as it is just
noise to normal users who are not debugging this problem.

spec/requests/topics_controller_spec.rb

@@ -3563,7 +3563,7 @@ RSpec.describe TopicsController do
 
     describe 'converting public topic to private message' do
       fab!(:topic) { Fabricate(:topic, user: user) }
-      fab!(:post) { Fabricate(:post, user: post_author1, topic: topic) }
+      fab!(:post) { Fabricate(:post, user: user, topic: topic) }
 
       it "raises an error when the user doesn't have permission to convert topic" do
         sign_in(user)