[Review]: Rotation improvements

An AIA submap is working but my HMI submap test is not working. More details to follow.

Assistance appreciated.
Argh.  Create another issue (or revive an old one).  Out of scope for this PR (which is to fix bugs!).

We have to have a separate discussion of the use cases of recenter, because I feel that once we improve Map so it can do proper coordinate-aware addition/subtraction and improve `rotate()` so that it doesn't crop out data, we don't really need recenter.

Regarding a potential `shift()` function, I presume it would have the capability of changing the correspondence between data and pixels, while `recenter` does not change this correspondence.