QRegularExpression::match() always copies QString created with QString::fromRawData()

The QString::fromRawData() documentation indicates how to use QRegularExpression with a QString without making a copy if using raw data.

Unfortunately, this is not possible since QRegularExpressionPrivate::doMatch() uses QString::utf16() which does the copying in this case (as indicated in the documentation of `QString::fromRawData()`).

PCRE2 doesn't need a 0-terminated string since it takes a size. Qt6 uses a QStringView which does not have this problem with utf16().