API: Fix ApiFormatFeedWrapper

With recent changes to the API, directly outputting text from execute()
in ApiFormatBase subclasses doesn't work anymore. Adjust
ApiFormatFeedWrapper for this new situation, and also handle headers in
initPrinter() where that belongs.

Bug: 72359
Change-Id: I4e4a2386858da6d87169deabaca763eeeacefbe9
(cherry picked from commit e80638ccff7ac1cb2976902f4b8c54e45849e9e5)