[InputFilter] Port QRegExp to QRegularExpression
Summary:
Port QRegExp::exactMatch() by using QRegularExpression::anchoredPattern().
Construct one QRE object to be reused inside e.g. a for loop.
For string concatenantion use QLatin1String where appropriate.
Test Plan: It compiles
Reviewers: Konversation, psn, hein
Reviewed By: Konversation, psn
Differential Revision: https://phabricator.kde.org/D28319