Fix broken HolidayRegion::rawHolidays*() API added in KF 5.95

See individual commits for details (the first three in particular, ie. two of the new methods don't work as advertised, a third one wasn't even implemented at all). This was noticed by libraries/kopeninghours!96 (closed) (is nobody else using this API yet??).

@dfaure At least the three first commits would seem important for 5.97 if that's still possible?