[platforms/virtual] Set raw physical size of outputs
Summary: At least one test requires the physical size to be set.
Test Plan:
Lock screen screen edges test is passing again. Without the change the corner
offset in the ScreenEdges class is not calculated correctly via the
physicalDpiX() and physicalDpiY() values of an auxilliary QWidget.
Reviewers: KWin, davidedmundson
Reviewed By: KWin, davidedmundson
Subscribers: davidedmundson, kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D15183