Re-organize issue move method calls

Move method calls related to execution of moving an issue into separate
private mothods. The reason is that then these methods can be easily
extended with EE specific code
(https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/4550#note_59158691).

Related gitlab-ce#41949

app/services/issues/move_service.rb

@@ -19,19 +19,10 @@ module Issues
       # on rewriting notes (unfolding references)
       #
       ActiveRecord::Base.transaction do
-        # New issue tasks
-        #
         @new_issue = create_new_issue
 
-        rewrite_notes
-        rewrite_issue_award_emoji
-        add_note_moved_from
-
-        # Old issue tasks
-        #
-        add_note_moved_to
-        close_issue
-        mark_as_moved
+        update_new_issue
+        update_old_issue
       end
 
       notify_participants
@@ -41,6 +32,18 @@ module Issues
 
     private
 
+    def update_new_issue
+      rewrite_notes
+      rewrite_issue_award_emoji
+      add_note_moved_from
+    end
+
+    def update_old_issue
+      add_note_moved_to
+      close_issue
+      mark_as_moved
+    end
+
     def create_new_issue
       new_params = { id: nil, iid: nil, label_ids: cloneable_label_ids,
                      milestone_id: cloneable_milestone_id,