[Applet/Task Manager] Move audio indicator to the corner

Summary:
When vertical or Icon-only task manager, shrink click area 10% and
indicator 30%.
This allows moving it closer to the corner, away from the center,
to avoid accidental audio muting.

BUG: 416553
FIXED-IN: 5.19.0

Test Plan:
With patch

Reviewers: VDG, Plasma, hein, ngraham

Reviewed By: VDG, ngraham

Subscribers: broulik, Fuchs, ndavis, filipf, cblack, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D26861