Examples should show idiomatic use of Qt and C++, so mark the custom
widget constructors in this example as explicit and their destructors
are override.
Amends 2690822428deec4f0c08f4d118d69a7c6036369e, which, however,
inherited the missing explicit from older code.
Pick-to: 6.8
Change-Id: I5b5b49f69330c6f139345bed7264c85a36c36e9b
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit e0e9a5627376e04aba1b2ca2591554851d7de240)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
cc1af8409a