Port template highlighting to KF5::SyntaxHighlighter
Summary:
Besides a better highlighting and more accurate spell-checking areas, this
also removes the last user of the old highlighting framework in KDE PIM.
Reviewers: KDE PIM, mlaurent
Reviewed By: KDE PIM, mlaurent
Tags: KDE PIM
Differential Revision: https://phabricator.kde.org/D7674