Locked difficulty and difficulty lock cannot be narrated

After enabling the difficulty lock, the difficulty and difficulty lock buttons become disabled. This means that the narrator won't narrate these two buttons after locking, and the narrator.button.difficulty_lock.locked message is unused as a result since it only is used as a narration in a state that never gets narrated.

This issue poses problems for people who use the narrator to interact with the user interface, because the narrator will not read the difficulty when it is locked. With keyboard navigation, the difficulty information will be skipped over entirely.