this allows e.g. popupapplet to put constraints on where the edges of the window can resize to
and react differently when the user is actively resizing the dialog.
CCBUG:227095
in this way we can use the corona to actually find out the real desktop geometry, that doesn't fail for extended monitors like QDesktopWidget does.
BUG:257955
svn path=/trunk/KDE/kdelibs/; revision=1207416