Its methods act on their parameters without changing the converter, so
can all be const. Its instances thus have no non-const members to
exercise, so can always be const.
Task-number: QTBUG-111228
Change-Id: Ifcdb2f2159c2cfcd7998dd118aa327a32d299ccf
Reviewed-by: Dennis Oberst <dennis.oberst@qt.io>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
(cherry picked from commit 77fdd21cbf1a053efe6eec51356c665ed982d47c)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>