gdksurface-win32.c: Fix display of CSD windows

gdksurface-win32.c: Fix display of CSD windows

Since the changes to GDK to use surface subtypes, CSD windows were
broken because we did not set the window styles properly.  Fix this by
first acquiring whether decorations are used by the GtkWindow, and based
on that result we set the decorations that we want to use accordingly
and so apply them.

Thanks to Matt Jakeman for investigating into the issue and providing
pointers to a proposed fix.

Fixes issue #3157, besides the part where window sizes are not correct
since that is likely caused a separate issue.