Provide cursor geometry in device-independent pixels

QImage::size() returns the size of the cursor image in the native
pixels. We cannot use it as the cursor size.

(cherry picked from commit 170a0b63)

cursor.cpp

@@ -145,7 +145,7 @@ void Cursor::slotKGlobalSettingsNotifyChange(int type, int arg)
 
 QRect Cursor::geometry() const
 {
-    return QRect(m_pos - hotspot(), image().size());
+    return rect().translated(m_pos - hotspot());
 }
 
 QRect Cursor::rect() const