QSortFilterProxyModel::filterRegExp is going to go away in Qt6,
so port over to use QRegularExpression instead.
This required some changes where setFilterWildcard/FixedString()
was being used, as those would instantiate QRegExp based filters
in Qt 5, and will use QRegularExpression in Qt 6. Use the generic
setFilterRegularExpression here, to keep things portable between
5 and 6.
Change-Id: I6379be781aa3821b10ba783c088f82c1a0970911
Reviewed-by: Eike Ziller <eike.ziller@qt.io>