Cleanup QDataWidgetMapper/QFileIconProvider/ItemEditorFactory autotests:
- use range-based for loops
- use nullptr
- use member initialization
- use new signal/slot syntax
- use static invocations
- use override
Change-Id: I1a36ea2da7de1cfa5d5d4e305ef508fda3a6c460
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>