[ChangeLog][QtCore][QFuture] Added QtFuture::makeReadyVoidFuture()
and QtFuture::makeReadyValueFuture().
Basically, these methods behave like QtFuture::makeReadyFuture(), but
QtFuture::makeReadyValueFuture() does not have a "const QList<T> &"
specialization returning QFuture<T> instead of QFuture<QList<T>>,
which allows it to always behave consistently.
This patch also introduces usage of the new methods around qtbase.
Task-number: QTBUG-109677
Change-Id: I89df8b26d82c192baad69efb5df517a8b182995f
Reviewed-by: Marc Mutz <marc.mutz@qt.io>