Resolves: rhbz#1278885 gtk3 allocated size doesn't match configure-event size

so LibreOffice thinks its window is smaller than what gtk3 has allocated
for it.

For gtk3 (like firefox does) split size and position handling, leave
position/move handling to the configureEvent, but listen to sizeAllocate
and use that for the size handling.

Leave gtk2 as it always was

(cherry picked from commit 6adfbe62)

Change-Id: Ic52d6971595741ed658247b651e9e16c2ef9ed0b
Reviewed-on: https://gerrit.libreoffice.org/19924Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>

vcl/inc/unx/gtk/gtkframe.hxx

@@ -239,6 +239,7 @@ class GtkSalFrame : public SalFrame, public X11WindowProvider
 #if GTK_CHECK_VERSION(3,0,0)
     static gboolean     signalDraw( GtkWidget*, cairo_t *cr, gpointer );
     static void         signalFlagsChanged( GtkWidget*, GtkStateFlags, gpointer );
+    static void         sizeAllocated(GtkWidget*, GdkRectangle *pAllocation, gpointer frame);
 #if GTK_CHECK_VERSION(3,14,0)
     static void         gestureSwipe(GtkGestureSwipe* gesture, gdouble velocity_x, gdouble velocity_y, gpointer frame);
     static void         gestureLongPress(GtkGestureLongPress* gesture, gpointer frame);