Enable Unicode support in QRegularExpression where needed
This fixes a QRegExp to QRegularExpression porting bug; QRegExp was always Unicode-aware, whereas with QRegularExpression we need to enable Unicode support by setting QRegularExpression::UseUnicodePropertiesOption.
Add a couple of unit tests (and remove some code that's been commented out since 2005, time to bury it, I think).
Make regex with long patterns static, now the regex engine needs to parse it only once.