try to improve painting height for text lines - bug 403868 avoid to cut _ and other parts still broken: double height things like mixed english/arab, see bug 404713

Summary: using a better height and removing the overpainting stuff

Test Plan: I did try a bit to zoom and use different documents, it looks ok, but it did look ok before in most cases, too :/

Reviewers: dhaumann

Reviewed By: dhaumann

Subscribers: loh.tar, thomassc, kwrite-devel, kde-frameworks-devel

Tags: Kate, Frameworks

Differential Revision: https://phabricator.kde.org/D19283