Port QRegExp to QRegularExpression

Summary:
With QRegularExpression, a "-" character inside a character class, [],
indicates a range; one way to match a literal "-" inside [] is to escape
it "\-". See https://perldoc.perl.org/perlre.html

Test Plan: make && ctest

Reviewers: Plasma, apol

Reviewed By: apol

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D26359