Summary:
Currently, when displaying pager labels (either number or name), text legibility is
often poor or even non-existent, because the label is drawn below things that can
and frequently do obscure it.

This patch puts the label on top, so it's always legible.

Test Plan:
Before, displaying VD/Activity number: {F6795368, size=full}

After, displaying VD/Activity number: {F6800760, size=full}

Before, displaying VD/Activity name: {F6795367, size=full}

After, displaying VD/Activity name: {F6800754, size=full}

Reviewers: #vdg, #plasma, hein

Reviewed By: #plasma, hein

Subscribers: filipf, abetts, ndavis, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D20851