Make QPA think the tabbox is the active window
Summary:
Without pretendingn to activate the Window, Qt will not send
the right signals for accessibility, thus screen readers not working.
Reviewers: kwin, davidedmundson
Reviewed By: davidedmundson
Subscribers: graesslin, davidedmundson
Tags: KWin
Differential Revision: https://phabricator.kde.org/D16664