Commit 6ebe3d0f0806069f906522dfe9b81baa3f3478de introduced extra
SFINAE checks on the template conditions.
However, it broke the case of using callables with deduced return
type, because SFINAE does not work for such conditions and treated
as a hard error instead.
Fix by explicitly providing all template parameters, so that compiler
could figure a better overload on its own.
Only QtConcurrent::blockingMapped() seems to be affected, but add
unit-tests to check all other methods as well.
Fixes: QTBUG-130766
Pick-to: 6.9 6.8 6.5
Change-Id: I1ddbe712d8ce04ac96ba13841cb569d728cfb943
Reviewed-by: Tatiana Borisova <tatiana.borisova@qt.io>
f73765682e