* use nullptr
* use member init
* set ExpandingFieldsGrow fieldGrowthPolicy for QFormLayout, which
makes it behaviors similar on macOS as other platforms
* select first row to make up/down keys works by default
Pick-to: 6.5 6.6
Change-Id: I25d9869d2ca1c7274c2b750aada8270734787546
Reviewed-by: Liang Qi <liang.qi@qt.io>
ed1fbc7a88