support icon.width/height

Summary:
support the icon size hint of the control. Reinstate it in ToolButton
and add the support for the other controls
CCBUG:417514

Test Plan:
possible to control buttons icon sizes
mediacontroller taskbar tooltip with icons set to small:

Reviewers: Plasma, broulik

Reviewed By: Plasma, broulik

Subscribers: broulik, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D27396