Add modeSize getter

Summary:
The getter pixelSize rotates the size of the mode. In contrast modeSize just
directly returns the current mode size.

Test Plan: Compiles

Reviewers: #kwin, zzag

Reviewed By: #kwin, zzag

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D25901

abstract_wayland_output.cpp

@@ -88,6 +88,11 @@ void AbstractWaylandOutput::setGlobalPos(const QPoint &pos)
     }
 }
 
+QSize AbstractWaylandOutput::modeSize() const
+{
+    return m_waylandOutputDevice->pixelSize();
+}
+
 QSize AbstractWaylandOutput::pixelSize() const
 {
     return orientateSize(m_waylandOutputDevice->pixelSize());

abstract_wayland_output.h

@@ -73,7 +73,11 @@ public:
     QString name() const override;
     QByteArray uuid() const override;
 
+    QSize modeSize() const;
+
+    // TODO: The name is ambiguous. Rename this function.
     QSize pixelSize() const;
+
     qreal scale() const override;
 
     /**