Fixup merge of downloadType from 5.10.1

In 5.11 we deprecated downloadType and at the same time ripped out most
of the faulty logic. Later we partially fixed the logic in 5.10.1, but
kept the 5.11 version during the merge. This restores the improved logic
from 5.10.1, while keeping the property deprecated since it is still
misleading at times.

Change-Id: I12ee09a2b212506f7ba1a336c9c2e88aa3b1de24
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: Jüri Valdmann <juri.valdmann@qt.io>
Reviewed-by: Michal Klocek <michal.klocek@qt.io>