[showdesktop][minimzeall] Reduce the maximum panel icon size
Summary: The current size of the showdesktop/minimzeall widget is much larger than it needs to be. This patch reduces the maximum size in panels to smallMedium (22px).
Test Plan:
Before:
After:
Reviewed By: VDG, Plasma, mart
Subscribers: mart, ngraham, broulik, rikmills, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D21593