馃崚 yet more QRect right() fixes
QRect::right and topRight are off by one for historical reasons. This caused incorrect default positioning when a (new) screen gets enabled and automatically positioned.
To solve this entire source of problems let's stop using the faulty API and instead calculate the offsets manually. More code but no trap doors. The original code was written as though things were not off by one anyway.
(cherry picked from commit fb0c1657)