Address review comments

app/helpers/notes_helper.rb

app/mailers/emails/notes.rb

app/models/concerns/discussion_on_diff.rb

app/models/concerns/note_on_diff.rb

app/models/concerns/noteable.rb

app/models/concerns/resolvable_discussion.rb

app/models/concerns/resolvable_note.rb

app/models/diff_discussion.rb

app/models/discussion.rb

app/models/discussion_note.rb

app/models/individual_note_discussion.rb

app/models/legacy_diff_discussion.rb

app/models/legacy_diff_note.rb

app/models/merge_request.rb

app/models/note.rb

app/models/out_of_context_discussion.rb

app/models/sent_notification.rb

app/models/simple_discussion.rb

app/services/notes/build_service.rb

app/services/notes/create_service.rb