Widget meta types are not registered in static builds, causing a crash of statically linked Designer

qRegisterWidgetsVariant() is never called in static builds, causing the below Designer crash when querying a QSizePolicy property on startup.

Unsuccessful attempt at fixing it: https://codereview.qt-project.org/#change,40939

0 qt_message_fatal qlogging.cpp 863 0x1401d601d
1 QMessageLogger::fatal qlogging.cpp 358 0x1401d3f3d
2 qt_assert_x qglobal.cpp 1960 0x1401cf911
3 `anonymous namespace'::dummyConstruct qvariant.cpp 763 0x14018e3c5
4 QVariant::create qvariant.cpp 1100 0x14018ec11
5 QVariant::QVariant qvariant.cpp 1413 0x14018eeff
6 QMetaProperty::read qmetaobject.cpp 2817 0x1401b2960
7 `anonymous namespace'::QDesignerMetaProperty::read qdesigner_introspection.cpp 125 0x13f5c140e
8 QDesignerPropertySheet::metaProperty qdesigner_propertysheet.cpp 1088 0x13f5514b9
9 QDesignerPropertySheet::property qdesigner_propertysheet.cpp 1079 0x13f5513ca
10 qdesigner_internal::WidgetDataBase::defaultPropertyValues widgetdatabase.cpp 455 0x13f5b9a95
11 qdesigner_internal::WidgetDataBase::grabDefaultPropertyValues widgetdatabase.cpp 467 0x13f5b9bbb
12 qdesigner_internal::QDesignerIntegrationPrivate::initializePlugins abstractintegration.cpp 579 0x13f56205d
13 QDesignerIntegration::initializePlugins abstractintegration.cpp 762 0x13f562be3
14 QDesignerComponents::initializePlugins qdesigner_components.cpp 133 0x13f3eaed3
15 QDesignerWorkbench::QDesignerWorkbench qdesigner_workbench.cpp 194 0x13f29876a
16 QDesigner::initialize qdesigner.cpp 241 0x13f290357
17 QDesigner::QDesigner qdesigner.cpp 99 0x13f28f109
18 main main.cpp 55 0x13f28ef15
19 WinMain qtmain_win.cpp 131 0x14048391d
20 __tmainCRTStartup crtexe.c 547 0x140480156
21 WinMainCRTStartup crtexe.c 371 0x14047fe4e
22 BaseThreadInitThunk kernel32 0x777ef56d
23 RtlUserThreadStart ntdll 0x77923281