[Kickoff] Redo tab bar separator's geometry
Summary:
This patch makes Kickoff tab indicators glide (patch D22108) on the tab bar separator in all 4 orientations.
I had to give up on the separator matching the width\height of the tab indicators because it was just never pixel perfect.
Test Plan:
Screenshots made with patch D22108 applied
Reviewers: Plasma, VDG, ndavis, ngraham
Reviewed By: VDG, ndavis, ngraham
Subscribers: ngraham, ndavis, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D22128