HTC has installed but "hidden" apps before (in a way that cannot be unhidden), it is not uncommon for them. I don't really understand WHY they would do such a thing, though. Mirror was present and hidden in the previous (pre-JB) Evo LTE also. That said, I just performed a search in applications and it does not appear. It also does not appear in the "ALL" listing of apps in settings. But when I use the Google search bar, it appears, so it is certainly installed.
I used QuickShortCutMaker and found the app (has a stupid camera icon, like before) and placed it on a home screen for access. Used the attached icon.