widget: Use enum for orientation_mode

widget: Use enum for orientation_mode

This was proposed by Dave on the ML, I think it makes sense. Right now
the enum is just like the boolean, feature-wise, but it makes more sense
semantically (mode is not a bool) and allows for future extension (eg.
only apply orientation update for landscape vs. portrait modes).

There is absolutely zero testing for this in our existing codebase. Yay.