contentsMargins is a Q_PROPERTY on a QLayout. Qt 6.1 introduced
QLayout::unsetContentsMargins() to reset the contents margins to the
"default" ones (that the user can't know); that's the textbook
description of a RESET function for the property.
Add some tests also for unsetContentsMargins.
[ChangeLog][QtWidgets][QLayout] The unsetContentsMargins() function now
acts as the RESET function for the contentsMargins property.
Change-Id: I463d88363c11f4a15ad3d6af71401d8698de1d41
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
284d4e7125