Get output position and scale from output device interface
Let the data saved in OutputDeviceInterface be the single source of truth
and as low hanging fruits first do this for global position and scale.
Test Plan: Nested Wayland, Drm, virtual backends tested.
Reviewers: KWin, davidedmundson
Reviewed By: KWin, davidedmundson
Subscribers: davidedmundson, kwin
Maniphest Tasks: T11459
Differential Revision: https://phabricator.kde.org/D23489