QRegularExpression was introduced in Qt 5 as a better replacement for
QRegExp. In Qt 6.0 QRegExp is removed entirely.
To remain forward compatible with Qt 6.0, we can transition over to
using QRegularExpression.
Since this is inside a string literal, backslashes that are part of
regex syntax have to be escaped. But that's ugly, so convert to a raw
string instead.
