Properly change buttons hit area to enforce Fitts law when windows are...

Properly change buttons hit area to enforce Fitts law when windows are quick-tiled and or vertically/horizontally maximiezed. At the same time, do not draw the window round corners.

Summary: CCBUG:383434

Reviewers: ngraham, graesslin

Reviewed By: ngraham

Subscribers: Zren, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D7355