Updates BNumberFormat to be able to format
percentages. Also re-introduces some unit
tests and updates the BNumberFormat ones.
This doesn't actually fix#16312 as the
defaults for percentage formatting don't seem
to track the selected language, but goes part
way there.
Related to #16312
Change-Id: Id6ddf426ce5571f4e8513c0eb1663cf42ac53cb1
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3767
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>
564de1924a