I wrongly thought QSFPM::setFilterCaseSensitivity() would work when a
QRegularExpression was used, but that method only pertains to QRegExp.
Instead to get case-insensitive filtering set QRegularExpression::CaseInsensitiveOption
on the QRegularExpression object used with setFilterRegularExpression().
Also, thinking about this some more, no need to use QRegularExpression::escape()
with the QuickSelectDialog since only (\w| ) are accepted by the dialog,
everything else is gobbled up by the eventFilter().