Added ThemeHint::TabAllWidgets as a mean to access that platform
specific bool. The default implementation returns always true when
querying QPlatformTheme::themeHint().
Several auto-tests had to be updated to reflect for qt_tab_all_widgets'
type change. One XFAIL removed from tst_QApplication::focusChanged().
Task-number: QTBUG-24372
Change-Id: Ie1f0486c19898fe54c53aa4a27e378485075e512
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>
06332df743