fdo#45935: try hard to paint a frame for menus

Current Oxygen theme doesn't draw frames for menus, but uses shaped
and "colored" background images. This workaround paints the window
and menu frame for menus. Any frame seems to be better then no frame
at all.

Change-Id: I4d553ea58cac2729826f8395cb2597fa200187b6
(cherry picked from commit e72849cd435cc50a744dcbcfb422f5600dd0cce9)
Reviewed-on: https://gerrit.libreoffice.org/8436
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>