win32: Ensure we always send a configure event when changing size/pos

win32: Ensure we always send a configure event when changing size/pos

There are some cases where we don't get a WINDOWPOSCHANGE such that
we generate a configure event, even if we called gdk_window_move_resize()
or similar. For instance:
* The window is fullscreen
* The window is maximized
* The specified pos/size is the same as the current one

However, as per X11 ConfigureNotify semantics we *always* want one, or
we could run into issue like e.g. bug #537296 where we're waiting for
the CONFIGURE to call gdk_window_thaw_toplevel_updates_libgtk_only().