Account for QPolygonF type when loading/saving the QVariant

When the QPolygonF type was added to QMetaType it did not bump up the
values in load() and save() for QVariant.

Task-number: QTBUG-33981

Change-Id: I7ad99cda70620c5449c15527c3daf920972d047f
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>
QFileDialog: don't create widgets if the platform dialog will be used

This is a performance and memory optimization which also fixes bugs
that are related to creating widgets, file system models etc.
despite using platform native dialogs.  Similar to
785bc64f8e743ac269f15cbe7fecba93d3d507ac for QColorDialog.

Task-number: QTBUG-33039
Change-Id: Ia1aa7ec1f43b47006b9ebd377aed15c958538a17
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>