Use Transform enum internally
Summary:
Instead of using Qt::ScreenOrientation use an enum class that is directly
mapped to KWayland's transformation enums. This simplifies the code.
Test Plan: Compiles and transformations work as before.
Reviewers: KWin, zzag
Reviewed By: KWin, zzag
Subscribers: zzag, kwin
Tags: KWin
Maniphest Tasks: T11670
Differential Revision: https://phabricator.kde.org/D25558